@Fransiska Hi. Are you able to login into Tusky yet? I guess the problem is that you can find this instance at the beginning. So, when they ask you "which instance", you need to type exactly "mastodon1.artsrn.ualberta.ca". Then our instance will appear for you to login by email. Pls set up an meeting with me via google meet if you need more support.
One more thing is that I recommended you to use Tooot on Android. It allow you to send direct message.