Bought domain name & hosting from same company - not sure what to do next?

I recently bought a domain name and a hosting package from a company. I logged into my hosting account and typed in my domain name where it said ‘add domain’. When I type the domain name to look at it on the web the page says it cannot be reached.

I uploaded a index.html page but still that’s not showing up.

When I added my name a window came up saying I had to get registrar details. But if my domain was bought with this company shouldn’t it just… work?

I feel really stupid not being able to work this out, must be obvious for somebody out there? I’d appreciate any help straight away, thank you so much!