Help me understand this concept, two overpair hands.

[JackThree]

i played this hand today.
limped in CO with 6d 4d, button folded~
flop comes 4c Jd 6s
a guy in ep bets, a couple of callers in front of me, i think "hmm i have two pair, i should raise" but the part in SSHE "two overpair hands" has the hand with TT you know, and it says to wait til the turn to see if the card is safe or not. and i'm wondering if i should call or raise this flop.

can someone please explain if that applies here or not and why, also if you're feeling generous give me another example where it does apply?

any help is greatly appreciated
thanks.