Weather strip for a garage door. I got the 15ft pack at Lowe's. You can get plastic or foam, but the foam is best, as it bends should you scrub your bumper.
3m double sided tape. Try to find black so it matches your strip and won't show as bad.
You can cut this stuff with scissors easily, so no tool is required. And you'll need some screws with washers on them to help hold it on. Something like this..
Your first step is to apply your 3m tape on the back of the strip. Space it out unless you bought two packs. It won't cover the whole thing.
When you get tape on the back of it, start putting it in place across the bottom of your bumper. Peel the backing off the tape as you go. The tape will hold, but for it to really last, you need to put some screws in it.
I put six in mine evenly spaced.
Hope I covered everything. If you have any questions feel free to ask.