The miner actually uses your CPU for finding a block, then you get added in a miner-witness queue where the witness needs to "witness" a block when its turn comes (becomes 1st in the queue) and just after that you can get a reward. The mining process here is a bit more complex as it is not just a simple POW (proof of work) like with many other crypto currencies.

In the end you need to have both a witness and a miner, but if mining with multiple PCs you can have multiple miners and just a single witness.