Why to use Discord?Following chart explains it better than thousand words.
Where can I get Discord?Navigate to
https://discordapp.com/ and choose Download from top navigation bar
How can I join server?After you have installed your Discord application you are able to
Create and
Join server.

When you choose
Join you get screen which asks you to add invite key. Those keys are:
AAO25 -server: Key =
https://discord.gg/0qGhTzjmdVrDllnvAAO25 Scrim -server: Key =
https://discord.gg/0qGxC6ataavLXFRvI have joined, what next?After you join to AAO25 -server you get screen like this. Well actually your screen looks a bit different than mine, since Im not using default colour theme. So there are colour themes: light ( = default ) and dark. You can change these from bottom left corner of your application window, there by right side of your name you can see three buttons. Mute, Deafen and
User Settings. Pay attention for these User Settings, from there you can set all push to talk, key binds, account details etc.

As you can see from picture above, there are quite many #textchannels. When you join there you see only #general and #news. This is because of roles and role privileges.
What are roles?There can be numerous of different roles and every role can have different privileges. Basically in these AAO25 and AAO25 Scrim servers there are three different kind of roles. Admin, Clan member and Normal User. From this image you see there is Admin role, and then there is a list of clans marked in yellow. They are roles defined to clans and each clan has similar roles when compared to each other.
For what are these roles for?With roles we can decide which group of people has access and power in which channel. Basically clan has all the access for their own Voice & Text channels.
Like this image shows, there are no global permissions defined...
...but as a member of clan and with clan role you get permissions to your channel
Why there are two servers?Simply because of the amount of channels and the lack of TS3 kind of hierarchy. Not all of us needs scrim channel so these channels can be elsewhere. In AAO25 Scrim server you can join only to those channels where your role allows you to join. So there are no password requirements - privileges are defined by the role.

AAO25 server is made to be as a lighter and new generation alternative for ts.aao25.com where players could meet each other. Mobile app makes this be like a good mixture of TS3 and Whatsapp.
Windows users might need to run application as Administrator to be able to run it in correct way while playing.