Just bought the Monster Manual...

Just bought the Monster Manual to be able to have a few creatures that my druid may summon/turn into. I can not for the life of me figure out how to add it to current game I'm running. Please help.

Once you buy it, it is in EVERY game you have on Roll20. Go in the game to the compendium (Top right black circe with the information " i " in the center) and from there type in "creature" or "monster" or whatever.

If you aren't the creator/co-GM of the game you may need to get them to enable the compendium in that game before you can see it. Failing that you could create your own game, drop all the options into it to create the sheets and export them to the vault for importing to your game as and when you need them (assuming the creator has enable vault access of course ;) ).