I've seen a few different posts about "Seafoam", basically sounding like its function is too clean carbon buildup.
I'm doing a full tune-up tomorrow

Plugs
Wires
Cap
Rotor
Filters
etc.

A - What is its function exactly
B - Is it really worth it?
C - If so, where do you buy it?

 

" Seafoam is a motor treatment and fuel conditioner originally developed in the 1930's by Fred Fandrei for Evinrude Outboard Motors. Originally named for its marine applications, seafoam is now widely used in the automotive after market.[1] Seafoam has a variety of gasoline and diesel engine applications including the reduction of carbon buildup, moisture and varnish. It can be used to treat gas tanks, fuel systems, and crankcases. Applications Seafoam can be used through the injection or carburetor to clean carbon buildup, which will restore power and pick-up to the engine. The fuel system can also be cleaned by adding the seafoam to the fuel tank, which conditions the fuel and removes moisture. Seafoam can also be added to the crankcase to remove moisture and clean dirty parts, increasing R.P.M.'s and compression.[2]"

When you buy it read the directions.

A simple GOOGLE search would net you the information you seak. Try your local AutoParts store. Advanced Auto Parts, AutoZone, Etc...