Partial recursive function and Turing machine
You first define what a partial recursive function is, and then what a Turing machine is.  Then you show that for every set (problem), there is a Turing machine computing it if and only if it is definable by a partial recursive function.

What you actually would do is to simulate a Turing machine by a partial recursive function and vice versa.  Right to left is simple, left to right takes some work.  You must define an encoding of the machine states (use of e.g. powers of prime numbers), the transition function, a configuration of a machine (i.e., what is currently on the tape, where is the head, and in which state is the machine) etc.