GMATPrep and the old version (PowerPrep) do not come with explanations. You can search for questions that have already been posted and discussed here and you can also post questions yourself.

NOTE: be careful only to read the ones you've already done! You don't want to "spoil" your future practice tests by seeing some of the questions in advance!

For most efficient review, first do a search with quotes around a few not-too-common words from the test of the problem. If that problem has already been posted, you may find that whatever has already been discussed is sufficient to answer your questions.

If you find that the problem has been posted, but the discussion doesn't answer your question, please add you question to that existing post. Ideally, we'd like to keep discussion of a single problem within a single thread.

If the problem has not yet been posted, feel free to create a new post containing that problem. (Please be sure tto follow the forum rules when posting - cite the source, type in full text of problem and answers, give us a detailed question as to what, exactly, is giving you trouble with the problem, etc.)