apple airport express

[#1]

trying to setup an airport express instead of the supplied router but struggling to get it to connect to t'internet.
set it up as pppoe and entered my username and password that's in my router, am I missing something?

[#2]

I've got an an airport extreme and that was all that was required.
Assume you're on fibre?

[#3]

I just setup and airport express this weekend to extend my wireless network. Just use the Airport Utility on your Mac or Windows device to set it up.
How are you connecting the airport express device to your router, the router will still need to stay connected to your ADSL or Fibre connection.