You use it to edit your photos on your computer then you upload the finished product to your photobucket account.
Open the program and you'll see these tabs across the top. File, Edit, Image, Options, View, and Help. Click File then Open and then look where you have your pix and choose the one you want to resize. Once you have it opened click the Image tab and then choose Resize/Resample. That will open a new window titled Resize/Resample Image and there will be a few options there that will let you choose how you want to resize your image. By Height and Width, Percentage, or preset sizes. Choose an option then click OK at the bottom. Your image will then be resized.
If it suits you click File again and choose Save As. Then rename your new image and save it where you can find it.
If it doesn't suit you click File and choose Reopen to go through the process again without any changes made to your image thus far.
That should get you on your way. If you have any problems let me or someone else know. It's easy once you get the hang of it.