To download custom albums in the Words app, go to the Library and tap "Download More At myOsmo" under "Installed" (the top section of the Library). You'll be redirected to the myWords page of the myOsmo website.
Select any of the albums and tap "Add to Words game". You'll be prompted to open the album in the Words game.
Tap the album to include it in the game (and don't forget to deselect the albums that you don't want to be included).
Then go back to the home screen, tap "Play", and choose any mode to play the album(s) that you have selected.
Find more information about custom albums in our PDF guide to the Words app here: