How Do Websites Make Money?

[Neil]

"I hear of ppl saying "Google" pays them money for their website. How does that work."

Through Google Adsense but to be successful you need hundreds if not thousands of websites all with Google Adsense on them.

"Do companies just pay you to put there ad up or do they actually pay you like per click or per sign up."
No- you have to achieve sales for them & then they pay you a commission.

"Can they check it? Speaking of which, how do I myself check how many visitors my page gets"
There are websites which can check the popularity of another site. If you're hosting has Cpanel, check Awstats within your Cpanel or join Google Analytics and register your website.