I'm the farthest thing from a magic know it all, so I have a question for you. If my opponent has a 40/40 with trample and I have a 20/20 with lifelink that is blocking it. and I have 20 life left. Do I gain life from lifelink at the same time the damage is dealt to me? Thanks for taking the time to answer!
Yes, lifelink is not a triggered ability like you might expect but a static replacement effect that replaces damage being dealt with the damage being dealt and you gaining that much life:
119.3f Damage dealt by a source with lifelink causes that source’s controller to gain that much life, in addition to the damage’s other results.
702.15a Lifelink is a static ability.
Note that this is not the case with cards that say "Whenever this card deals damage, you gain that much life"; that would be a triggered ability, and you would lose before it could resolve.