How to know if something is a scam?

Like for example I went on Craigslist and it took me to this website saying I won a prize like either a new iPhone or ipad. I just skipped it because of the high risk it might be a scam. But I was wondering because the only information they asked me to give out was my e-mail address.could it still be a scam? Also how often does it happen to people that they give even the littlest information and then get no prize or worst into trouble?

A lot of times these are legit - but you have to read the fine print. Usually there are other sub-offers that you must complete before the original offer will be given. The hope is that you complete some or all of the offers which will more than pay for the iPhone or iPad that you'd eventually get.
You can always set up a separate email for these types of things so if you start getting spammed, it won't affect your primary email account.
Hope this helps!

It's a SCAM. There are NO websites that give free iphones, free ipads, free laptops, etc. These are all phishing scams and spammers trying to get your email address
Never click on these links - if you did you should run a virus scan and Malwarebytes as those links are often infected