How to remove errors on the site?

Have any of you had experience creating and promoting websites? I'm still new to this topic and have run into one problem that I can't solve in any way. What do I need to do in order to eliminate errors that often creep into the site?

Yes, I have taught myself how to create websites, so I have faced this problem many times. Now I can fix it without any problems, because I found out about the service, where you can use the website error checker https://pr-cy.io/ I am sure that you will also understand everything, because the site is described in more detail