Playing Adult Interactive Fiction (AIF) can be seen as a three-step process: First, finding the game you want to play. Then, for most games you will need a custom interpreter to play the game, and lastly some knowledge on how to manipulate the game world.
When it comes to finding games to play, this Wiki is a good start. If you're looking for specific content, most of them have dedicated categories to make it easier to find. The next step is finding an interpreter capable of playing the file on your platform.
The People's Republic of Interactive Fiction have created a placard showing the most commonly implemented actions in IF. For AIF it's common to have more focus on clothing and body part, as well as actions/verbs that focus more on the Adult part of the genre. Most games are nice enough to give some mention on which actions and body parts are used, and some even have built-in HINT or HELP commands to get you started. DeusExLibris has also written a guide for new AIF players.