The questions you are asking are fundamental QA questions. I suggest reading any basic testing book. For instance "Automated Software Testing" by Dustin, Rashka, and Paul is a good one and will answer many of your questions, also "Software Testing" by Patton is also another good one. Try these books and then if you still have more questions we will gladly answer them. It is just hard to explain the fundamentals on this board. Especially since there are complete books on the subjects you are asking about.
Simple minds, Simple thoughts!
I figure if you have the courage to get out of bed in the morning, then how bad can the day be.
I will start by giving you one or so answer to each because this is a very broad subject.
Environment can be enterpreted in many different ways you can be talking of database environment, OS, and it also depends on what kind of program you will be testing. We test all of our environments the same Sql 7, Sql 2000, windows 2000 profesional and server, XP, 98, Terminal server, NT, Etc...