I downloaded the pack. What do I do to add them to dsl.
You just take the files from the zip or rar into the intended location. If you install AI pack, you have to put it into your AI folder. Be warned however that AI packs tend to overwrite any existing AI on your game, so if you want to keep the old AI, make a copy of the game and then install the new AI pack into the copy
to clarify open up the .zip or .rar you downloaded (extract the AI folder) and copy the AI folder into your main RA2 folder. it'll ask you if you want to merge or overwrite, say yes. if it doesn't ask this then you've put it in the wrong place.
make completely sure that you've downloaded an AI pack for the correct mod you're using or it'll crash your game. some packs overwrite the old AI, and some just add more, they should say in the description. I would highly recommend making a second copy of ra2 for another AI pack. just duplicate your ra2 folder and call it like "DSL [mod]" or whatever. i have 20 different ra2 versions with different mods and ai packs. don't put everything on one copy, trust me.