malloc() and calloc() return pointers to allocated memory,
or NULL on failure.  The memory so allocated remains allocated
until the process calls free() on it.  If you forget to
call free, or simply have a bug, you create a "memory leak."
If you leak enough memory you will run out.  Most programs
die when that happens.

It is important to note that C lets you name the memory
that are the 8 bytes reserved to hold the current value
of a pointer, and it lets you separately name the memory
the pointer points at.  For

int *p;

you say "p" and "*p" to mean those two things, respectively.
So, you store the pointer returned by malloc or calloc in p.
The memory allocated is at *p.