I am unable to adjust the size of my finder window! Any tips on recovering the bottom right hand corner?! Thanks

Sometimes. clicking the green button in the upper left will toggle a window to a smaller size.

Also, look at System Preferences > Universal Access and select the "Seeing" tab. Make sure "Zoom" is turned off:

iMacs with different hardware configs go all the way back to 1998 and that can affect troubleshooting advice. Can you please tell us which model you have and what OS it's running in case the above suggestion do not work. If you do not know these, do "About this Mac" from your Apple menu and tell us what it says for "Processor" and Mac OS version:

Once you have this info, it;s a good idea to place it in the equipment information in your user profile, Gets you help much faster,