Very very complicated question, because sub Saharan Africa covers such a large area. Ethiopia, Mali and Sudan have a very different history to South Africa and Botswana.

But ok, lets start from the beginning.

The first contact between sub Saharans and European almost certainly happened in Europe. The Kushite empire from Sudan conquered Egypt and fought a series of wars in the levant area (Israel, Jordan and Palestine) that are mentioned in the bible during the 8th and 7th century bc. During that era, kushite temples were built in Cyprus so undoubtedly there was contact. In any case the kushites had their own writing system, they built great statues but they were highly influenced by the Egyptians in those respects (they built sphinxes and used hieroglyphs and so in sources like the bible, the kushites were seen as more Egyptian than Sudanese).

The greeks used the term Aethiopia to refer to sub Saharan Africa on the east coast. That is modern day Ethiopia, Eritrea, Djibouti, Somalia and Sudan. The first greek visitors there probably happened in around the 6th century BC. They mention that the natives there were pretty advanced, they were literate by then and formed their own states.

The second great sub Saharan empire, after the Kushites, was Axum in Ethiopia. Mani, the Iranian prophet who founded the religion of Manichaeism, spoke of the four great powers of the 3rd century as being China, Rome, Persia and Ethiopa.

Axum was very much linked into the european trade network, Rome was sitting in Egypt at the time, from where it sent trading misisons to asia and the African east coast. And both Rome and Axum fought wars against the nubians in the sudan. Ethiopian coins printed from the period use greek letters and when the roman empire received reports of jewish warlords attacking Christians in yemen they asked axum to intervene. The man who converted Axum to Christianity, Frumentius, was a greek speaking roman citizen who travelled to Ethiopia on a trading mission and whose story was written about by Italian historians.

Axum was a literate centralized state which had iron, built obelixs and cities, printed it's own coins, fought on equal terms against persia and traded not just with Europe and India but through out sub saharan Africa. Goods from axum reached right the way to the atlantic coast.

During the same period Somali sailors traded with India and China, on one hand, and then rome on the other. And made a fortune as middlemen. Romans actually believed that cinnamon was a Somali spice because that there was their main source of it, they didn't realise the Somalis were just buying it from the Indians.

Romans traders undoubtedly went further down the Swahili coast and traded in Tanzania, Kenya, maybe even Mozambique. According to our main sources on this, the somalian and ethiopian towns sold goods (dyed cloaks, cups, iron sheets) but the ones further south mostly only sold materials (ivory and tortoise shells) which indicates a much less advanced society.

The fall of rome and then the arab conquests cut off the Swahili coast and the horn of Africa from Europe until the age of exploration. Not entirely, Ethiopian priests travelled to Jerusalem during the crusader kingdom there and the king of aragon exchanged letters with the emperor of ethiopia during the early 1400s but mostly sub Saharan Africa didn't have any new contact with Europe until the Portuguese explorations from 1444 to 1500.

There is however one important exception here. We've been mostly dealing with the east coast because you could sail there from Arabia and Egypt. There were sea voyages down the west coast from carthage in tunisia but not much from Europe. Western sub Saharan Africa didn't really have massive contact with the Mediterranean world until the introduction of the camel in the 3rd century ad allowed the trans Saharan trade to kick off. Which means our main sources on the Sahel (Mauritania, Mali, Niger, Chad etc.) are muslims from muslim north Africa. However this does include muslims from muslim spain in Europe. It's probable that Spanish muslims visited the sahel in the 10th and 11th centures ad.

They would find a series of relatively large empires (Ghana than Mali than Songhai) with little centralised control and no history of writing until that was introduced by arabs. They weren't as advanced as the Ethiopians (they seem to be have a primary barter based currency rather than using coins, though they did use gold nuggets) but they did use metal, build with stone, have a court system with rules of law and have large armies. And though they weren't literate until conversion to islam, mali became a great center of literature.

So that's pre Portuguese european contact with Africa, which is mostly the relatively advanced northern kingdoms just south of the sahara.

Portugal circumnavigated the entire coast. Mostly they'd have encountered pre state, pre literate people. Large parts of sub Saharan Africa wasn't advanced. They did also encounter the Mali empire and reinitiate contact with Ethiopia and Somalia but mostly you're talking quite primitive people. Not completely primitive, they had agriculture, domesticated animals and metal and were more likely to live in towns than be nomadic, but not hugely advanced.

There were states to be found though, and I'll cover the three major exceptions that the portuguese encountered who were more advanced in more detail, though they were not the only states to be found outside the sahel and the horn of africa.

One: the Swahili city states in Kenya, Mozambique and Tanzania, the Swahili didn't have gunpowder (we have chinese sources of Swahili kings being impressed by it) but they lived in cities, they were great sailors who traded regularly with india and china, they were literate and they built impressive mosques. Again like the sahel, they'd advanced largely through interaction with the Islamic world, which is where they got writing from.

Two: the Kingdom of Mutapa in Zimbabwe, who weren't literate but had a centralised state with regular trade with asia. The portugese both traded and warred with them and discovered the ruins of great stone cities, which impressed them as being far superior to any of the still used cities in the region.

And, most importantly, the Kingdom of Kongo in Angola. They were a highly developed state at the center of an extensive trading network. They made metal goods and dyed cloth and their capital was the largest city in sub Saharan Africa. However again they weren't literate, writing and building in stone seems to be things they picked up from Portugal, albeit quickly in both cases.

Coins seem to have rarely travelled south of Ethiopia, which has used them since the 3nd century ad. Most sub saharan Africans used either barter or sea shells as a universal currency (the exceptions which did use coins, seem limited to Somalia and kilwa in tanzania). Likewise written languages were mostly confined to Sudan, Ethiopia and countries who'd converted to islam and used the Arabic script. Metal working (including iron) pretty much had spread everywhere. Building in Stone reached Zimbabwe but not Kongo.

It varied by area, basically.