It's pretty easy, just take a propane torch, heat up the top real good, (make sure you coat the wire with flux before you put it in the terminal), and then start filling the top with solder. Then I like to take the flame to the outside of the terminal, because doing that flows the solder down into the ring, and provides a stronger hold. I use a loot of solder on my terminals. And then I just fill the top in when I'm done, sometimes having to grind off the extra.