This is how i was taught infinity back in 6th grade (maybe seventh) in a proof logic and reasoning course:
First, imagine you have a hotel with one floor and infinitly many rooms. Now lets say you put people in every room. Now say five more people come in asking for rooms, what do you do? Tell everyone to move five rooms over. Now you ask, "But I thought every room was full!?!?!" My answer to you is, mention one person who cannot find a new room? The guy in room one will now be in room 6, they guy in room 100000000 will now be in room 100000005. Therefore infinity + x = infinity. Now to continue, lets say infinity people come to the door? Everyone cannot move down infinity rooms because they will be walking forever. What you do, right after your head explodes, is tell everybody to move over by their room number. There for, everybody still has a room, and there is now room for the new infinity people.
So ends my first situation.
Now for my second:
So long as you can match every number in one set with a number in the other set, there is an equal number of mebers, Correct? Now, make your integer set look like this: {0,-1,1,-2,2...} and your natural number set look like this: {1,2,3,4,5...} Quikly we can see that every integer is accounted for by every natural number so these sets are equal. What about rational numbers you say? well make your set look like this:
1/1 2/1 3/1...
1/2 2/2 3/2...
1/3 2/3 3/3...
. . .
. . .
. . .
Granted some numbers are repeated butthat would only make the set larger now smaller so i don't even bother thining of them. Now if we walk through this set making concentric square we once again have every number in the rational accounted for by naturals, and therefore the sets are equal. This is the smallest set of infinity hence its name aleph-not, the hebrew letter alef with a small zero to its lower right. Now natural numbers cannot be organized like this and are there fore a different level of infinity and are given the name aleph-one, you can guess the symbol. Past this I dont know, haven't taken calculus yet. But this is a good way to explain infinity in almost laymans terms.
BTW, this is my first post, if there is something fundamentally wrong in my manner of posting please tell me