How to put in links in header menu?

Hi there,

I am pretty sure this is going to be easy but for some reason I cannot work this out. I am messing around with a new theme…it can be found here..
https://theriverkelvin.co.uk/themetest/

What I want to do is actually use those links under the header but to go to an external site. I have found the code here

<ul id="navlist">
<li><a>">Home</a></li>
<li><a href="">Link1</a></li>
<li><a href="">Link2</a></li>
<li><a href="">Link3</a></li>
<li><a href="">Link4</a></li>
I thought it woudl be as simple as https://www.blahblah.com but it doesnt seem to work..

Help ??

Alistair