If you're wanting to learn about air pressure and your looking for practical science practise here are 5 experiments to try...
How to squeeze a hardboiled egg into a bottle
Make your own hovercraft - A really fun hands on project and a great homemade toy.
Self crushing can experiment
Submarines - how they work and an experiment to go with it.
The self inflating Balloon
Vacuum in a glass
How to turn a glass of water upside down without spilling it in three easy steps
Diet coke and Mentos explosion! - possibly the most fun explosive action you can get at home!