The Instructions on how to play a match are detailed on the website on the FAQ page :-

“How do we play a match?“

https://u3achessnetwork.org.uk/laeguefaq

Here are some screen shots to illustrate exactly how it works …
I want to play a friend “nickhomboy” .. Click on CHALLENGE in my Friends list..

Challenge

Then select the correct time control 15|10 in this case and press PLAY

Now it waits for your opponent to accept …

Your opponent should see your CHALLENGE in their screen….

After your opponent accepts the challenge the game should start up ..