Germanic tribes were the peoples of Southern Scandinavia and what is now Northern Germany and the Netherlands. The Roman historian Tacitus gives a remarkably detailed picture of them around AD 100, from knowledge gained from his father in law, the Roman general Agricola. They knew a bit of farming, and kept livestock. They worshipped many gods, including Tiw, Woden and Thunor (Thor) that Tuesday, Wednesday and Thursday are named after. They gave the warrior high status, thought it disgraceful to flee the battlefield, and were ruled by ‘kings’. They had no real ‘towns’ and farmed in woodland clearings.
They can be split in terms of geographical area/related languages to East Germanic (the Goths, Vandals, Gepids and Burgundians), North Germanic (the Norse or Norwegians, Danes, Swedes and the later Icelanders) and West Germanic (the Franks, Angles, Saxons, Frisii, Langobards (Lombards), etc.)
Their move into the Roman Empire in the 4th, 5th and 6th centuries AD, under pressure from the Huns to the east, is considered to mark the start of the European Dark Ages. From the chaotic times of the 5th century, things eventually settled down and kingdoms like England, France, Denmark and Germany (for many centuries the so-called Holy Roman Empire) owe their origins to Germanic tribes. Regions like Lombardy (Italy) and Burgundy (France) preserve some of their lost names.