Rejiboy,
I've never really had satisfactory results painting (large areas) with brushes. I always use my airbrush (a Badger internal mix single action and a Badger double action), but if you must paint larger areas such as car bodies or planes, then use spray cans. There are a number of companies that have some of their range in spray cans (like Tamiya, or Testors or others), and you should use those.
Brush painting a car body or an aircraft fuselage and wings will get the color on, but you'll probably be unhappy with the results - it'll be streaky and you'll see brush marks.
When you spray, make sure you spray on a warmish day with little humidity, and heat the can in a pan of warm water (this increases the pressure within the can) as this help spray distribution.
Start off the model and spray past the model - don't start to spray and finish uour stroke "on" the model as you'll get an uneven finish or runs.
Try to gain a little practice on card stock or tin cans before you attempt painting the model - better to get some experience before you attack the model.
Remember - practice and patience are probably the two most important tools a good modeller has in their toolbox. There's no magic about it.......we've all learned because we've made mistakes. You'll make them, too, and each model you make will be better than the last one. And don't forget to have fun, mate.
I also very strongly recommend subscribing to Finescale Modeler - it's a bloody good mag - they often have articles on the basics of things like painting, decaling, filling gaps, making vac form models - stuff like that. It's made me a better modeller.
Cheers,
LeeTree