When you first sign up for an account here, you will be emailed a password. You can use that password as long as you like. however, if you're like most people, you have a password you use for random crap like blogs and newspaper sites. You probably can't remember the crazy password that's emailed to you either. The way to fix that is to change your password!
So, after you login using the emailed password, do you see up there in the top right-hand corner where it says "Howdy (your name)"? If you click on that and then "Edit Profile" you will be taken to a "Profile Page". At the bottom of that page, there's a place to change your password to something a little more memorable.
There are also numerous "lost pasword" links all over the place if you need those. Failing that, email email@example.com and I'll help you out.