isn't it like say i got 10 bucks in the pot already and its 40 bucks another guy calls 10 [...]
Just remember, in terms of pot odds, you don't count money you already put in the pot. That money isn't yours anymore! So in the example you gave it would count as 5:1 not 5:2.

Implied odds are pretty touchy and it's a bit of a guessing game and it's about how well you know the other players at the table. If you call, is the next guy going to raise you? Is the guy after him going to go all-in? What about on the turn or on the river? Fun stuff.