Furniture, Wood and Cabinetry Finishing - Kitchen cabinets

I am going to re-finish my oak cabinets. I have never done this before and unsure what needs to be done. What is the best sand paper to use and the best stain to use? Do I also need to clean them with something?

Here is a link the "how-to" for refinishing cabinets:

http://www.doityourself.com/scat/cabinetrefacing

There is a sublink there for "staining cabinets" which will tell you everything you need.

Prep work is key to a good outcome.

Proper cleaning with a product like TSB or similiar will remove the grease and oils from the surface. Once cleaned, start sanding down with 220 grit paper then clean again. I could go on further, but check out that link I provided to get you started.

My cabinets seem to have faded over the years and some seem to have almost yellowed. Would a stain & polyurethane work the best for this or would something else work better to make them all the same color?

A complete stripping and sanding to remove the existing finish is the only true way of getting a even, durable, and better looking finish.

Typically these projects consume alot of time and tedious work so prepare for it. Like I said earlier, preperation is key.