To develop APIs or services, and know how to hack them, you need to learn how to design algorithms, and know one or more programming languages.
There are several ways of designing and implementing programs. There are usually two ways. Either by using a compiler, which will transpose the source code into binary executable, directly comprehensible by the machine. Either by interpreting the code, ie the source code is read by an interpreter, which transposes the source code into instructions that can be understood by the computer.