Are resistance bands the answer?

Hi FB friends. I have been Blending for a few years and have seen a lot of good from this mild addiction :)

Here's my question though: I understand that if you keep doing the same workout and do not increase the weight you're lifting every time, the benefits are reduced? I only have a few dumbbell sizes and have been pretty much doing the same weights on exercises for a while.

Now, I can't really afford a new set of dumbbells. Can anyone explain resistance bands to me? I figure they may be an affordable solution, but can they really replace dumbbells? Is there a good tutorial on using them? How do I know what sizes etc. to get?