Sealer

I'm installing a stone tile that has a pourous surface. Someone said there should be some sealer put on tile before grouting to prevent grout from penetraiting tile. Is this correct and if so, what product?

There are plenty of stone sealers available. It would be helpfull to known which stone you are talking about.

Is this correct

Usually, yes.

I have a 12"X12" Scabas Random Pattern Mosaic Tumbled.
I had heard that it is to be set and dried then sealed before grouting. Thats all the info I have on the tile as my girlfriend bought it somewhere and brought it home.

Yes, you need to seal this before you grout with a penatrating sealer for stone.
Read instructions carefully

Stone tiles will absorb plenty of moisture from the thinset, so sealing the installed tiles shouldn't be done for a few days. Applying sealers to moisture-laden stone isn't a good idea.

Bud
What if the stone tiles listello's are going on the shower wall 1x2 inch pieces?

Stone is stone.

You run the risk of the stones turning milky. If you use a water based sealer then maybe not so much. BUT, the sealer must dry totally before it sees any shower water. Use a fan!