redhulkz, there are three very different kinds of natural resources in the game and you shouldn't confuse them. There's more details on pp63-64 of your manual. There's also something here on civfanatics, I think in the FAQ, but I would have to go find it.
To summarise:
Gold, which is a bonus resource just gives you extra money if you work that tile with a citizen. It does nothing 'special'. You cannot trade it.
Gems are one of several luxury resources or luxuries. They give variable bonuses if you work the tile (gems, for example, gives +4 money, just like gold). But gems also act to make your citizens happy if you link cities to them with a road, and you can trade your gems with other civs if you wish, which might net you more money, or tech, or other stuff.
Oil and rubber are both strategic resources. Not only do they, like luxuries, provide bonuses to a worked square, but they are required to produce certain units. Different units require different resources - so, for example, rubber is required for infantry, while oil is also needed for tanks. Most 'modern' ships need oil, but not rubber. So it all depends what you want to, or can, build. You can sometimes ask for a lot to trade these - however it may not be wise to give a potential enemy what he needs to build his forces. How much a civ gives for a strategic resource basically depends on how much it needs the resource. (This also applies to luxuries in trade, too).
Note that you can get, as well as give, stretegic or luxury resources in trade, if you don't have them in your territory.
Hope that helps.
ciao for now
