Unwanted “Comments” how do I stop them

Hello,
First I’m sorry if this question is in the wrong place, but when I log into my admin WP site, I notice there are a lot of unwanted comments in the “comments” section of the dashboard. First, how did they get there & second how do I stop them from coming in at all. Most of them are “ads” for insurance or porn. I have marked them as spam, but keep getting more.

Thanks.