Let's put it this way: What you did was being on the Internet. Sadly, spam is just a fact of life on the Internet. If there were a simple solution for getting rid of it, someone probably would have hit on it by now.
So, all you can really do is resign yourself to trying to manage the spam as best you can. Do as suggested and either mark it as spam or just delete it. NEVER respond to spam, even if it claims to be an unsubscribe link. That usually just gets you MORE spam. Also, be selective about to whom you give out your email address. One of the great thing about these free email services, is you can set up one or two used exclusively for signing up to websites or whatever else, where you may well get put on some junk mail list. You can log into the thing as needed, like if you signed up for some site and need to get login info, but otherwise the spam just collects in that account where it's no skin off your nose. Meanwhile, your primary account remains known to a rather select few people, which will limit the amount of spam you get to very manageable levels.
You may also want to read up on some of the common email based social engineering methods used by scammers. Like it's never going to happen that your bank or credit card company (or any other reputable company) is going to email you asking you to go to some website and log in to verify details. They will CALL you on the phone, and then if you have any doubts about whether or not the person really works for who they say they do, you can hang up, and call the main customer support number for the business and verify that there was some issue with your account.