Didn't mean to sound snappy.
To clarify, let's expand the line of code you don't really understand like so:
The first line is an if statement which compares the
variable (which is passed as an argument to the function) and the size in bytes of the
integral type, which we can safely assume to be 1 byte.
If the condition is met (that psize is equivalent to the size in bytes of a char), execution continues in the branch.
The second line instantiates a character pointer with the name
The third line initializes
to point to data which was passed as an arguement.
The fourth line increments the value of what
is pointing to by 1.
Will edit this if more information is requested.