How do you keep things from showing up on certain pages

[kobescoresagain]

I have some things that I have setup on my site, that I do not want to show up on things like logon pages, logout pages, redirects, and in certain forums. I know exactly what the code is, and where to find it. I also know that you would probably use an if else statement. I understand what an if else statement is, and the basics about it, but I don't know how I would go about this. How can I do this?