I've been looking for part-time jobs and I keep seeing these ads for jobs that you can do from home on the internet and get paid through your paypal account? Does anyone know anything about this type of employment? Is it legitimate?

Some are but I can’t promise that all are. I know someone who has done this before.

if they want you to buy anything before joining than its a scam, if its too good to be true it usually is. Do a research on the company before anything try better business bureau or the trade comission etc

Not many are legitimate. You can sometimes do customer service. You can definitely do medical transcription. Check the company by googling its name with the word complaints. Also check it with the Better Business Bureau.

Never do one where you have to pay them money first.

From personal experience, I advise against getting involved with that type of thing. I’ve never found one that wasn’t a pyramid scheme. And, as others have said, especially avoid the ones that ask you to pay some kind of fee in advance.