You have a dig command that you can use to manually dig resources out from the planet. Using science you can make a shovel and hand drill to increase your digging speed. Then you must collect enough to afford a big drill.
The only way to get super rich is to use a drill (not a hand drill). An upgraded drill can dig about a million times faster than you ever will be able to dig manually. Just use science to make the drill and then upgrade the drill using the resources that the drill digs up.
You can take resources out of your big drill by getting next to it and clicking it. You can upgrade it by right clicking it while next to it.
Drills must be protected or someone will steal them. So it is good to build a house around them with upgraded walls. The higher your knowledge is the higher you can upgrade your walls which makes them far harder to break. See the science section for info about knowledge.
Drills can not dig more than the planet has available. Other drills on the planet cause yours to not be able to dig as much since they are competing with each other for the planet's available resources, which the planet only refills at a certain rate.
The only other way to get rich with resources is to steal them. If you are powerful you can break someone's walls and steal the resources out of their drills. If you somehow managed to get a door hacker, which is rare, you can hack the door and do it that way too.
You can also steal from a knocked out player. See the stealing section.