You can get right to it by going to a local paint retailer (listed in the Yellow Pages under Paint Retailers) and bring a sample piece of garage with you (if you don't know what it is you're painting.) I suggest you DON'T use a Home Center's paint because of quality issues (I've personally experienced) with their paints. (They sell a brand-name's Competitive Brand in their store.)
The Retailers sell very good paint. Sherwinn-Williams, Benjamine Moore, and Finneran & Haley (my favorite) to name a few are the places where I buy my paint. Use a good Primer/Sealer if you're painting anything that can 'bleed' through. Personally, I'd do 2 coats of top-coat paint. (I'm not that good where I can get away with 1 coat.) Don't paint in direct sunlight if you can help it. Paint in T-shirt weather if possible. Use Latex primer and paint. Buy your supplies while you're at the retailer. And by all means, READ the can(s) before you leave the store to be sure they suit your needs. And, if you have any questions, you're right there.
If there's more, post up. My best to ya and hope this helps.