Hi Ann,
Welcome - and don't worry

that will be easy to solve.
You will need to get Mac OS X 10.4.11 Combo update.
http://support.apple.com/kb/TA24901 lists the versions.
If your Mac is an Intel based Mac, then use this link
http://support.apple.com/downloads/M...Update__Intel_
If it's a PPC based Mac, then this
http://support.apple.com/downloads/M...o_Update__PPC_
If you are not sure which Mac you have - which model is it? Someone will help you find out if in doubt. The Mac model will tell. (or About This Mac... from the Apple in upper left corner > the processor info. If it lists an Intel something, then it is an Intel based one)