Check your work. Access your homepage through the internet using your browser. If your page isn't quite right, you can continue to edit and upload until your happy with your work. Each format has it's advantages and disadvantages. Gif files can be saved with one color transparent such as this simple icon .
Jpg files have the ability to be compressed.
Scanned photo's should almost always be saved in jpg format while computer generated graphics usually do well in gif format. There are many graphics programs available for use, but very few freeware ones. The Corel Graphics Pack isn't cheap, but will do all you ever need to do. Microsoft has some programs available for downloading on a trial basis. Graphics on the net can be yours with a simple click of your right mouse button on them, but beware of using copyright material.