pot equity / fold equity

Can someone please explain to me pot equity and fold equity and its usefulness in hold em?

[Borodog]

Pot equity is your "share" of the pot, if all hands go to the river. For example, if you have A [img]/images/graemlins/club.gif[/img]K [img]/images/graemlins/club.gif[/img], the board is A[img]/images/graemlins/diamond.gif[/img] 7[img]/images/graemlins/club.gif[/img] 8[img]/images/graemlins/diamond.gif[/img], and two other players in the hand hold K[img]/images/graemlins/diamond.gif[/img] T:diamond and 9[img]/images/graemlins/heart.gif[/img] 6[img]/images/graemlins/heart.gif[/img], then your pot equity is 42.4%:

http://twodimes.net/h/?z=1331628
pokenum -h ac kc - kd td - 9h 6h -- ad 7c 8d
Holdem Hi: 903 enumerated boards containing 7c Ad 8d
cards win %win lose %lose tie %tie EV
Ac Kc 381 42.19 522 57.81 0 0.00 0.422
Kd Td 354 39.20 549 60.80 0 0.00 0.392
9h 6h 168 18.60 735 81.40 0 0.00 0.186

Fold equity is the chance that your opponent will fold his hand, and hence reliquish any share of the pot. The pot equity of the folded hand is then distributed proportionately to the remaining hands, although fold equity is usually discussed mainly for heads up pots.

[ QUOTE ]
Pot equity is your "share" of the pot, if all hands go to the river. For example, if you have A [img]/images/graemlins/club.gif[/img]K [img]/images/graemlins/club.gif[/img], the board is A[img]/images/graemlins/diamond.gif[/img] 7[img]/images/graemlins/club.gif[/img] 8[img]/images/graemlins/diamond.gif[/img], and two other players in the hand hold K[img]/images/graemlins/diamond.gif[/img] T:diamond and 9[img]/images/graemlins/heart.gif[/img] 6[img]/images/graemlins/heart.gif[/img], then your pot equity is 42.4%:

http://twodimes.net/h/?z=1331628
pokenum -h ac kc - kd td - 9h 6h -- ad 7c 8d
Holdem Hi: 903 enumerated boards containing 7c Ad 8d
cards win %win lose %lose tie %tie EV
Ac Kc 381 42.19 522 57.81 0 0.00 0.422
Kd Td 354 39.20 549 60.80 0 0.00 0.392
9h 6h 168 18.60 735 81.40 0 0.00 0.186


[/ QUOTE ]

How do i count that in my head?
what is the reason behind i get 42% equity?
does i have an advantage on 9%?? is that my pot equity?