Don't worry about it! We can still answer your question here ;-)
To (for example) associate jpeg files with the program of your choice, do this:
Right-click on the icon for any jpeg file.
Select 'Open with'
If you see the name of the program you want listed there, do NOT click on it. Instead, click on 'Choose program'
Put a tick in the box where it says 'Always use the selected program to open this kind of file'.
If the program you require is in the list shown, click on it and then on OK. If it's not shown, click 'Browse', navigate to the location of the program, and double-click on it.
Chris