Equity and pot odds question: Do I understand this?

[fluxrad]

Would it be relatively correct to say: Equity tells you when to bet an raise. Pot odds tells you when to call and when to fold.

There was another post that I completely screwed up so I'm trying to make sure I get this (i.e.):

You hold Q[img]/images/graemlins/heart.gif[/img]8[img]/images/graemlins/heart.gif[/img] in the BB.

3 people limp, and you check it.

Flop: (4SB) <font color="blue">(4 players)</font> 7[img]/images/graemlins/spade.gif[/img] T[img]/images/graemlins/heart.gif[/img] J[img]/images/graemlins/heart.gif[/img]

What's a good way to determine if you have enough equity to value-bet? Do you say "Well, I have 12 outs to make a straight or flush, meaning I'm good here more than 1/4th of the time so I should bet."

Let's say this pot is 3-way. Do you still have enough equity to bet this flop?

One of my major problems is figuring out when and where I should be thinking about equity. I'm hoping this might help clear it up.