Welcome to the Linux community. Most of the software is free and open source. Most of the people who utilize this software are good people who want to help you. However, there are a few people who are total dick heads and who want to fuck you over. So because of that we build security into most of the things that we produce. For instance, if you were confused by why it instructs you to run a checksum after you download the software, that is because the actual authors of the software want to make sure that you downloaded their legitimate software and not some hack bullshit posted by somebody else. A checksum is just comparison of what you have installed to what you're supposed to have installed and your computer will tell you if things don't match up.