every time i go on a global map for earth world i find some metal mines and some oil wells. How do i get them?

you have to attack them in order to capture them, they may be owned by other players, so watch out

Also the more mines you capture, the better off you are. The mines give you a big boost to your income and workers.

And what about the oil wells??

it's the same

Metal mine and Oil well both are Bonus outpost but they has some variations....

Metal mine : it gives +5 metal from each metal mine your alliance holds,

Oil well : +4 oil from each oil well your alliance holds

but both gives 0.5 worker per 24-tick.......