Realize a MAC using a Pseudo-random function? Given a pseudo-random function and assuming that we do not have any other tools,
How can we construct a MAC? 

I believe this can be done. Would like to know if there is more than one way of doing this.
If you have a PRF (with larger input than output), you can use it as compression function in a Merkle-Damgård structure, yielding a hash function which you can subsequently turn into a MAC with HMAC. Indeed, the security proof of HMAC relies on indistinguishability of the compression function from a PRF.

There are still an awful lot of details, though. And the PRF assumption is quite strong.