Starting at one side of the garage door attach the seal to the door bottom using one nail or screw at a time depending on whether your door is wooden or metal.
How to install bottom garage door seal on metal door.
Thread the t shaped edges into the weather seal track then slide the seal across the door.
Make sure you have the right weather seal for the retainer the retainer is the metal strip on the bottom of the garage door that has a track for the weather seal.
Install the new seal with the larger sloped edge to the outside of the garage door and the flat part against the bottom of the door.
If you have a wooden garage door rip off the nailed rubber seal.
He also gives a brief description.
Clean the door bottom photo 2 then cut the new rubber seal to length with a razor knife.
In this video we add a new aluminium retainer and new rubber seal.