This web page in the link below - one single page - contains all the basic information that you are now asking for. There is a chart there that explains exposure in the context of the "Sunny 16" rule. Read the web page and print out the chart and carry it with you whenever you carry a camera. If you follow its guidance, you will *always* produce reasonably well-exposed photographs.
Your Pentax is a pretty modern model with fairly advanced electronics inside. It reads a code on the film when you load it and sets the ISO for you.
Second the recommendation to get a book on basic photography. Despite what you say about all the reading you have done, you are asking the questions that would be asked only by someone who has either not done any reading, or did and understood none of it.
Edit to add: the web page takes the same basic theme of MESuper's excellent post into greater detail.
2nd edit to add: Same page. Forget what I said, just listen to him. He knows more and has more patience than I do, anyway.
Last edited by pbromaghin; 12-28-2011 at 01:27 PM. Click to view previous post history.