Header editing, I have to add text in header

Hello,
I would like to ask you for some help. I have been given an assignment to add text which leads to registration form of the website but I am completely new to php and that’s why I would like to ask you guys to help me do it.

I have to edit header.php and place text “Are you a vendor” which by click will lead to the registration form of the site when you are not logged in it. It should only appear when user is not logged in the website.

I just have to know some basic steps where should I search for this issue and solve it.

https://postimg.org/image/x50vgkjjn/

Kind regards, Nick.