I am sure this is an easy question for most of the guys on this site, but here goes.
I have a GM crate 350, long block I bought from Jegs, getting ready to set in. Changed the cam to a Comp XE268H, with their lifters. Eledbrock intake with tri power ready.
Question- What is a balancer, what is a dampner, what is the difference, what is internal balanced, does this all relate, and what size balancer do I need?
Thanks

Balancer and dampner are the same thing for what your asking.
350's are internally balanced.
Which long block (or it's number) did you buy ?
There should be an info page for that engine to tell you what you need for the balancer.
If not ,call Jeg's.

The info says "Timing tabs for a 6 1/2 or 8 inch balancer" So again, at the risk of sounding stupid, can I just buy any 6 1/2 or 8 inch balancer? Anything from Jegs will work? And is there a difference between the two? Believe it or not, I am a relatively intelligent 40 year old.

It'll depend on which timing tab came with the engine.
GM's had a variety of balancers over the years and each one goes with a particular timing tab.
As I don't know which tab/s you have ,can't say with accuracy which balancer you need.
Here's what I'm talking about & note the timing pointer positions:
http://paceperformance.com/index.asp?PageAction=VIEWCATS&Category=1293

Here is the engine I bought. Can I buy a 6 1/2 inch balancer. I feel like a 4th grader asking something that it seems I should know the answer to.
http://www.jegs.com/p/GM+Performance/752506/10002/-1
Thanks

From the Pace site I referred to:
Two timing pointers are also included, a pointer for a 6" balancer and a pointer for an 8' balancer.Balancer with 2:00 timing mark must be used with this engine in order for mark to line up with the pointer.
http://paceperformance.com/index.asp?PageAction=VIEWPROD&ProdID=224002

Got it, thanks Mike!

Spectre sells a universal timing tab for SBC balancers. This is assuming that your engine needs the tab on the 3 'oclock position on the timing cover and not the 12 O'clock or thereabouts that some later models need.

The only difference I can think in using a universal timing tab would seem to me to be the actual distance between the balancer and the tab. For a 6.5, it'd be higher above the tab, for an 8 in. the balancer would be closer to the tab.