You're asking a pretty big question, and it's important to remember that warfare will vary based on the time period, the people involved and the purpose of the conflict. It's very difficult to make an intelligent generalization about such a vast area and time period. Let me share with you some brief information about warfare in coastal Alaska between 1500 and 1800 CE.

Before Russian contact, the Kodiak archipelago likely was the most densely populated area of Alaska, with most estimates indicating about 15,000 people living across the archipelago. To put that figure into context, the entire Native population of Alaska in 1867 was probably 25,000. Today, the Kodiak archipelago has about 14,000 people.

That kind of population density generates conflict, and Kodiak was no stranger to war. Here's what the Alutiiq Museum has to say about warfare:

In classical Alutiiq society, where social positions were inherited and a small class of wealthy individuals acted as community leaders, warfare was a means of enhancing wealth. In addition to avenging wrongs, elite men led raids on other communities to acquire plunder and slaves, and increase their affluence. Neighboring Alutiiq communities were attacked, as well as more distant Aleut, Dena’ina and Tlingit villages. In battle, warriors carried short wooden clubs, spears, bows, and specially fashioned arrows. The arrows were tipped with bone points that had thin, splintery barbs. Craftsmen designed these barbs to cause extensive internal damage by breaking off inside their victims. In addition to weaponry, warriors carried large shields made from thick planks of hardwood and wore protective vests of wooden armor. Fashioned from small pieces of wood and tied together with sinew, these sturdy yet flexible shirts protected a warrior’s chest from enemy arrows. Warfare is a common topic in Alutiiq stories, where incidents leading to conflict often unfold in predictable ways. In many stories, visitors from a distant place ridicule and embarrass a community member—particularly a chief or a child. After the incident, community members secretly follow the offenders to their homes and take revenge, sometimes with the assistance of neighbors. These stories illustrate the types of events that led to conflict and probably reminded people about the consequences of cruel behavior. They also illustrate that the goal of conflict was not simply to punish the offender, as this could be done anywhere, but to separate the offenders from their possessions. By taking revenge in the offender’s home, raiders could acquire plunder.

One thing the Alutiiq Museum's description doesn't cover is slavery. War prisoners were commonly taken as slaves in Alutiiq warfare. In conflicts within the archipelago, these captives tended to be seen more as honor/peace hostages rather than outright slaves. When captives were taken from the mainland or Fox Islands, they were employed more as slaves.

Gavriil Ivanovich Davydov, who traveled to Alaska twice in the first decade of the 19th century (Two Voyages to Russian America, 1802-1807), is one of our best sources for this information. Ben Fitzhugh's The Evolution of Complex Hunter-Gatherers: Archaeological Evidence from the North Pacific collects a lot from Davydov and other sources.

Slaves were traded like commodities, exchanged for otter skins or dentalium shells, which were the principal currency in Kodiak. Slaves were typically women and children, because dying in battle was seen as preferable to capture and enslavement. The exception to this was honor hostages exchanged by two warring parties to ensure peace.

A 1790 visitor to Kodiak records that slaves were even killed at the death of a high-ranking elder in order to serve him in the afterlife. Davydov doesn't see this when he arrives 15 years later, though this may be attributed to the Russianization of the islands.

Let's go back to combat. This 1997 paper is a great read about warfare, though it is a technical document and may be difficult to understand by a layman. I'll summarize:

We believe the principal weapons of war were clubs and bows and arrows. Bows and arrows are not good tools for hunting sea mammals, so the prevailing theory is that they were tools of war, since they can be found on islands with no land mammals. The tips of some recovered arrows "...are thin, brittle, basalt fishtailed projectiles and have been interpreted as being specifically for snapping off in the body of an enemy leaving a jagged, infectious wound."

The prevailing pattern of warfare, as identified by the title of that paper, is "Raid, retreat, defend, repeat." Attackers arrived by kayak, landing some distance away from the attacked location, then sneaking overland for a surprise strike. Groups then retreated with captives. Attacks were almost uniformly by surprise.

Fortifications, usually well-defended rock pinnacles surrounded by ocean, were the best defense against these attacks. "Women and children occupied unscalable cliff areas and refuge islands for protection while the men were away hunting in the summer. If attacks were expected, everyone moved to these defensive sites. Young boys were trained in the ability to endure pain by being forced to stand in the freezing seawater and by ritually cutting their skin open with shell fragments. Russian naval officer Davydov was told that ‘‘in earlier times’’ prisoners were brought before them and, as their stomachs were cut open while still alive, children were expected to pull out their intestines. They were also expected, as the story goes, to stab them or use them for target practice with their bows and arrows."

Farther west than Kodiak, along the Bering Strait coast, Dorothy Jean Ray describes a similar set of circumstances in her book, The Eskimos of Bering Strait, 1650-1898. In that case, the raiding was done across the strait, with conflicts frequent enough between Siberian Eskimos and Alaskans that the oral histories of the raids survived to be recorded. We know there was (and still is) peaceful contact across the Strait, so we can't think of it as a front of constant conflict.

Instead, as in Southwestern Alaska, the conflicts likely were driven by feuds, territorial disputes, or the need to gather resources -- including slaves. One of the better-shared stories is that of the "last Siberian invasion," when the Alaskans defeated the attackers so soundly that they killed all but two, who were left alive to share what had happened to their counterparts.

As /u/The_Alaskan says, it really varies based on time period and geographical area.

For example, the Haida from the coast and islands of British Columbia saw warfare largely as a chance to capture slaves, and were experts in amphibious attacks from large war canoes.

The Iroquois on the other hand often went into battle not even trying to kill their enemies, but trying to capture them so that they could torture and sacrifice them later. This was not an uncommon desire among pre-Columbian native groups, and contributed in a way to their conquest by Europeans. The Aztecs for example had several chances to kill Hernan Cortes in battle, but did not because they were trying to capture him, not kill him.