Hold L2 to bring up the weapon inventory, then press Left on the D-Pad while holding L2 to bring the C4 in your hand. You can then press Left on the D-Pad without holding L2 to switch to the Mines.
Press L1 to throw a C4, then press R1 to blow it up.
Also L1 throws Mines, and you can pick them up again if they were thrown by wrong or weren't used by holding Square when you're right next to a Mine.
I'm not sure if C4's can be picked up again after they were thrown.