The gif or jpeg fomat is most universal and all of your images should be saved to these formats. BMP files are automatically changed to jpeg by Composer. The drop down menu under alignment allows you to choose left, center, or right alignment. Click on Color schemes button which gives a choice of attractive ready made color schemes. You can also pick the Location of an image you wish to use as a background - it should be subtle enough not to interfere with the text on the page.
Readability is the most important objective here.
Inserting a table allows you to organize information into a grid of rows and columns. You can also organize your links by placing them into the cells of the table. Alternatively, you can use button images to act as links. When you are finished with your HomePage and all of your links work, you are ready to show it to the world. Make one link to the classroom page you will create next.