The best way to get resources (RSS) to feed your castle's needs is to gather from the available resource tiles around you.
Gathering (or farming) refers to the process of collecting resources from resource spots (tiles) outside your castle. It should not be confused with plundering, which is the process of taking resources from another player (castle, tile or relic) following an attack. Gathering is not a complicated process and to a starting castle, is very important. Buildings and troops all require resources and your in-city production is going to be at a low level, so supplementing it with gathering will ease that burden. It is also the only way to get gems (apart from actually buying them or completing relevant competitions). As your castle grows, the resource needs also grow, so your gathering will continue to assist with this process.
For more information about the resource tiles themselves, please check out the Evony Basics topic, Resource Tiles.
Please also refer to the General's topic from the home screen.
You can send any General you like on a gathering expedition, however there are some Generals that will give you better returns if your invest in them.