Remove the cover/cap by pressing snap buttons and pulling off the cover/cap.
Remove the empty spool from housing and remember the orientation of the spool to install it correctly once you’ve filled it with trimmer line.
Look for an arrow on one of the spool flanges. This is the correct direction the line is to be wound onto the spool.
Look for a hole or slot to hold the line close to the hub/inside of the spool.
Press/lock the line into the hole or slot. Then, wrap the line around the spool in the direction of the arrow on the spool. Be sure not to overwind/fill the spool.
Holding the line, place the end of the line through the eyelet(s) in the housing.
Secure the spool correctly into the housing. Most spools have a gear shape side that should go in first.