To build new bases, you will first need to find more mines. Use your scouts to look around if you can find any. if you do not have any mines you can reach by land, build a shipyard and a freighter. Then load your scouts in a freighter, unload them on the other side of the river/sea, and go scout there. After you have found another oil, with ore in the neighbourhood, you will want to build a base there.
This is how you do it:
Click on your factory and build 3 transports. Once they are built, click on each transport, then right click on your command center. You can now add ore to your transports. Fill each of them up with 750 ore and 250 fuel. Then move your transports to the oil mine you found. Do the same with a builder. If you cannot move your transports and builder there over land, put them in a freighter. Always put the transports near the place where you want to build, so the builder has ore available. Then build the oil mine. Once this is done you need to build a command center, the hub of your new base. If you have found an iron mine near the oil, you should try to build the command center in such a way that the iron falls within the command center radius, the green wide circle you see when you select a command center. If this is possible, then simply build the iron mine and your next base is up and running. If this is not possible, you will have to construct a supply route. First click on main menu, bottom centre of your screen, then click on supply routes. After that click on create supply route. Then follow the instructions.
