Downloading levels is available from the start of the game. From the location selection screen, scroll and select "Downloaded Levels." Then tap the green globe button in the top right corner to be redirected to the web page with user created levels. Tap one that looks easy (i.e. not much going on, many of them are actually just levels where you push play to complete...) and wait for it to download to your device. You will then be sent back into the game where you can select the level you just downloaded to play it. Do whatever is necessary to collect the 3 stars to unlock this achievement.