Your answers, in order

1-The germans weren't just in germany anymore when Western Rome fell, what gives?

Well, after the Western Roman Empire fell, the many germanic tribes fleeing climate change and the encroachment of the Hunnic hordes, migrated across the formerly roman territory and estabilished kingdoms there, you may recognize a few of them

The Visigoths and Suebii took up residence in spain, where they mostly fought each other and their northern neighbors, the Franks.

The Vandals turned modern day Tunisia into a naval powerhouse, until pretty much the greatest strategist to ever grace the Byzantine empire, Belisarius, came and crushed them in a bid to retake the western half of the empire.

The Franks conquered their way through the remnants of the Roman Empire in modern day France.

The Ostrogoths formed up a powerful kingdom in Italy, only to be kicked out by Belisarius a few decades later, fresh off from beating the Vandals into submission, after the byzantines lost control of the region, the Lombards moved in and estabilished a pretty powerful kingdom there.

The Saxons led a slow, but steady migration to the British Isles and carved out several small kingdoms and contended over territory with the Romano-briton tribes that were left there after the romans abandoned the region.

These barbarian kingdoms basically laid the foundation to what was to become the great kingdoms of Europe in the middle ages, the Saxons eventually had their fair share of wars with the danes, swedes and norwegians and eventually created England, the Franks formed the Frankish Empire under the Merovingian dynasty and later the Carolingian dynasty that eventually laid the foundation to the idea that would become the Holy Roman Empire when Charlemagne was crowned Roman Emperor, having conquered a lot of german lands; and finally, the descendants of the Visigoths were locked in constant war with the many muslim invaders that had settled in spain in the century long struggle, later dubbed the Reconquista.

2- There were people living in germany back in the ancient days, how did they live?

Hard to say, what we do know is that the proto-germans (the term "germani" wouldnt be coined until about 250 years after the time you asked about) is mostly through archeological finds and such, those suggest that these people lived in northern germany, with the south being occupied by gallic tribes. Evidence suggests that the tribes in the region had Iron Age technology and were gradually moving towards their southern neighbors, who were eventually assimilated, but hard historical accounts on the region only start at about 50 B.C.

3- They spoke! But what did they spoke?

Well, it depends, for the 1000 B.C. to 500 B.C. germans, we literally don't know what they spoke, only that it came from the Indo-European family of languages.

As for the Post Roman germans, oh boy, we know a lot about their languages, mainly because literally the language I'm writing this on right now comes from one of them.

They spoke similar, but still distinct dialects of old german, which, with outside influences would end up becoming most of the northern european languages today.

The Franks spoke Frankish, which would be influenced by latin and saxon roots to go on to slowly but surely morph into Occitanian Provençal, French and Flemish.

The Saxon language brought over to Britain would mingle with the several other languages such as briton, norse and french to become English.

The old german language suffered a lot of changes when it started to become a written language, mainly because it took up the system used by the romans, and thus, was highly influenced by latin, even losing a couple of letters, such as the Thorn (Þ, it reads as a "th") there were some old german languages that developed their own relatively independent systems of writing such as the norse languages, that have said letters to this very day.

4- "Your sources, present them, fool!"

-the mods, probably

J.B. Bury: The Invasion of Europe by the Barbarians

Rosamond McKitterick: Carolingian Culture, Emulation and Innovation

https://www.britannica.com/place/Germany/History

Anita Salmoni: In Search of lost Languages (I'm sorry, I couldn't find a PDF in english of this anywhere, so no link)