If you want to find text adventures to play, you should look in the if-archive/games directory. There are three types of directories under this one:
System-specific game directories. These are games which run under one operating system. There are games for the PC, Mac, Amiga, and more. The games in these directories tend to be older ones, as most new text adventures fall in the next category.
Portable game directories. The game files for games written using text adventure languages are found in these directories under the if-archive/games directory. Game files are organized by the programming language used to create them. Some of the more popular languages are TADS (if-archive/games/tads), Inform (if-archive/games/zcode), and Hugo (if-archive/games/hugo). You'll need an interpreter to play these games; for TADS and Hugo, you can find one in the /executable directories that are in the programming section. For Inform, you'll need to look in the if-archive/infocom/interpreters directory. (More specifically, check the frotz and zip directories.)
Competition game directories. Every year there's a competition for text adventures that can be won in two hours or less. The games are kept in the following directories:
If you'd like to learn more about playing the games in all of these directories, read through Stephen Griffiths's FAQ about playing the Interactive Fiction Archive Games.
The archive has a number of hints and walkthroughs for text adventures. Most are in this main solutions directory, but files for the Universal Hint System, which gives hints rather than outright solutions, live in the if-archive/solutions/uhs directory.