For your second red heart, you'll need 100 rep points. To get the blue hearts, you'll start to have to accumulate 200 rep points. You can give rep by looking at the bottom of the post you wish to rep. You'll see a little star. Click on it, and select "Approve" (positive) or "Disapprove" (negative). Then you will have the option to leave a comment with it. We always suggest that you do, so people know why they deserved that rep. Never sign your name to a rep. Rep is meant to be anonymous.
Well, it's about 50 rep points per normal heart, then when you get your first container it's 100 points per heart container. I can't tell the exact numbers.