Note: This is all explained in C++, but the general logic should be the same if working in C.
It sounds like for both the intake code, and the clamp code, you want a hold button.
First, looking at the PROS documentation is incredibly valuable for knowing what to type for what actions, or detecting certain things. You could find it by clicking here. Make sure you are checking the documentation for YOUR version of PROS (the most current are versions 3 and 4, each having their own documentation)
You would want to put the following code into the opcontrol function, which should be in the main.cpp file.