How do you back up a Lap Top?

I really know next to nothing about backing up a Lap Top. I’m planning on buying an external Hard Drive from the store to back up ALL my data and important information, videos, movies etc. from my lap top to the hard drive once a week incase the laptop breaks or something. Can you please tell me everything I will need to know to do this, and just any general information, the more the marrier! And please don’t just copy/paste the info from a website =D.

I know this is a broad question but that’s because I don’t know much about this stuff.

I have a MacBook Pro 10.5.8, It’s total “Capacity” is 150gb and there is 50gb worth of space left on the computer. My goal is only to back up this information just incase my lap top ever breaks or gets stolen because my LIFE is on my laptop. I am planning to buy two external Hard Drives to be safe.

This is what I think I know, how I believe it all works, and the best way to do it – please correct what I have wrong:

So, all I do is go to the store, buy an external hard drive about 500 gb right? Someone said 1T is too much for a laptop, that it’s “Dangerous”, someone who does know about computers mind you. So anyways once I buy it, I simply connect it to my computer through a “firewire” instead of a usb since firewires are faster, (someone said) and I do this once a week to back up all the data from the lap top to the external hard drive and Presto! That’s it right? Anything else I should know about all of this?

please help, all answeres appreciated thank you!