Bicycle maintenance is generally easy. There are not many jobs that cannot be achieved by a home mechanic.
The following links go to the Park Tools website. They manufacture high quality workshop equipment. Their website is one of the most comprehensive on bicycle repair that you can find.
Changing an inner tube
Repairing the inner tube
Cleaning your chain
Cleaning your bike
Adjusting derailleur gears
Fitting a chain for derailleur gears
How to prevent your bike from being stolen (sponsored by Direct Line Insurance)
You can also find many helpful bike maintenance videos on YouTube.
Remember, if you don’t feel competent at carrying out repairs contact a bike shop. Your bicycle’s maintenance is critical to your safety!