In the beginning, you mostly need one thing: Resources. The timber camp cuts wood, the clay pit collects clay and the iron mine produces iron. The more you expand those buildings the more they produce. When you first join a world it is recommended to build up your resource production by a few levels.
After you have secured a good base production of resources you can start building troops. In the barracks (Level 3 Headquarters needed) you can start recruiting spear fighters. Spear fighters offer some protection against would-be attackers who might want to plunder your resources. They are not usually good attacking troops, but they are useful for raiding very small, undefended villages in order to plunder their resources.
In addition to recruiting troops, there are also other ways to help protect your village and defend your resources in the early stages of the game. One way to protect your resources is to build up your hiding place. The bigger the hiding place, the more resources are safe from attackers. Another good deterrent is to build a wall (Level 1 barracks needed). The higher your wall level the stronger your village's basic defense will be. This means your enemies will suffer higher losses when they attack villages with higher wall levels.
If you find you have excess resources, you might want to consider building a market. (Level 3 headquarters and level 2 warehouse needed). In the marketplace, you can see what your neighbors are offering and trade away resources you don't want. You can also create your own offers.
You should also look around your area to find a good tribe to join. It is always easier to fight and defend in a group. It is also a good way to meet some nice people!