You have three new pieces – two magnetic and one compression. The magnetic pieces are for your lock jamb and head jamb, compression piece is for your hinge jamb.
1. Pull out your old weatherstrip and discard.
2. Start with one of the long magnetic pieces and push the flange into the kerf (cut) in the lock side jamb down at the sill. Since weatherstrip shrinks a little over time, push the weatherstrip down tight against the sill, as this is the point we don’t want to ever leak. Use a wood block or other smooth hard object to seat the weatherstrip as you work your way up the jamb. Use a utility knife or scissors to cut the excess at the top.
3. Repeat the procedure with the compression strip on your hinge jamb (the other vertical jamb).
4. Install the last magnetic weatherstrip piece into the head jamb, cutting the excess with a utility knife.
5. Now go outside the door, armed with a putty knife. Close the door and check to be sure the weatherstrip is making good contact all around. Where it is not, use the putty knife to move the weatherstrip out from the jamb a little to get good contact with the door. You are finished!