On large commercial sites, it is important to change your password when you first log in. At home, you may not even have a password, but you should. Use the passwd command to change your password. It asks for your old password and then prompts you for your new password twice.
As any other manual will tell you, choose a password that does not include any real words in any language. Don't try to combine words, either. One of the easiest ways to get a good password is to pick a sentence, produce an acronym from it, and then modify the acronym with a number or some punctuation. All you have to do is remember the sentence. For example, Ayht8irt is a modification of the previous sentence.
You can change your shell with the chsh command, but keep in mind that this book assumes that you're running bash.