This YouTube video by This Old House runs through some of the basics of how to assemble and install garage doors yourself.
The bottom panel is installed first and can be the trickiest. The first set of hinges and brackets are affixed along with the weather stripping at the bottom.
The bottom panel is centered in the garage door opening. Rollers go into the hinges on each side. Recruiting a friend will help with this.
Tracks are then aligned on each side over the rollers and secured at the bottom. Tracks hang out at a slight angle only until the rest of the panels are in place.
Each door section is layered on top of the first with only one roller on one side installed. After it’s placed into the tracks, the hinge and roller on the other side can be installed. The horizontal track must be installed before the transitional panel can be installed.
The door must be manually lifted all the way and secured into place before the spring can be installed. Cables get attached to the bottom bracket and threaded through the pullies on each side. Do not forget to install the safety cable inside the spring.
Once installed, the door can be closed.