First, the AP6521 is only supported on the WiNG-5 platform. If you were attempting to use documentation based on WiNG-7, this potentially may have caused some issues when using the instructions - although the CLI command syntax is nearly identical between WiNG-5 and 7, there are certain features that only exist in WiNG-7.
If you locate a guide that is based on WiNG-5, any instructions and commands should work exactly as intended.
And depending upon which version of WiNG-5 is installed, it may have 1 of 2 different GUI's. The CLI syntax would still be exactly the same though. Note though, the original Flash based GUI will require a system that still has Flash capability in order to access the Flash GUI - otherwise, you would need access to the Extreme portal where you can download and install a utility that provides Flash access (WiNG Manager tool). The newer GUI is HTML5 and is referenced as the WiNG Express GUI and began being seen on non-Express model AP's somewhere around WiNG-5.7 I believe. (speaking of....is the AP6521 that you have an Express model? There is an AP6521E and a regular AP6521. On the back, it's label would show a model name. If it's an express model, then that creates a different situation - but the short answer is that the Express model APs can now be upgraded to full Enterprise WiNG mode)
There is a GUI wizard in WiNG-5 that will walk you through getting a basis setup. Once completed, you can then tweak the configurations as needed using the regular GUI or CLI. The AP needs to be booted up in a defaulted state in order to have the wizard appear though.
Here is a link that shows the Flash based wizard walk through.
There is also a wizard in the WiNG Express GUI, but I don't have any video references for that version.
