Most aluminum siding joins together like vinyl, which means that in order to make a repair, you'll need to patch a damaged area or replace a panel. This tutorial shows you both techniques.
Be aware that metal corner caps are sometimes used instead of corner posts for aluminum siding, and in older installations they were often used for wood or hardboard lap siding as well. If your local supplier does not have caps to match the ones on your house, check online sources; it helps if you know the manufacturer's name. In a pinch you can cut and shape a piece of sheet metal to fit, using an old cap as a template.
Also know that aluminum siding can and should be painted. Scrape any flaking paint, and sand smooth. Pressure-wash and allow to dry. Apply an alcohol-base primer, or an oil-base primer that has been thinned with 2 cups of thinner per gallon of primer. Apply acrylic paint.
Most repairs will take less than an hour, and you'll only need simple cutting and measuring skills. Before you begin, check the siding closely for further damage to determine how large a section of siding needs to be replaced.