It's very simple: locate in the Master Index the entry which most closely matches the practical question you wish to explore, or the subject that is of interest.
Click on the link. In case you need to visit more than one, each target page has a link back to the Master Index page so that you can later visit the other(s).
Having chosen a subject or question, you'll be led to a second-level Index of all the related entries we have found. Explore those at your leisure, and the job is done. Remember that understanding evolved over time, so recent entries are likely to give better information than older ones - which, however, form a priceless foundation.
ISMIS is dynamic - new entries are regularly added. So bookmark it, and try it first even if there was no answer to a particular question the last time you looked.
Occasionally, it will happen that the answers found in the materials or posts indexed do not suffice; for example, when the IRS tries a new trick, not previously encountered. So while ISMIS is meant to be the Zedhead's first resource, it's not his only one.
So read the indexed chapter(s), listen to the indexed tape(s) and review the indexed copies of TFN posts.
Then (and only then) the next step is to post the question to SSC.
Finally (and please do NOT do this earlier; Irwin's staff are extremely busy) call Freedom Books for help, on (702) 385-6920. A fee may be charged.