Tusky app is ok. I use it on a daily basis. Where did you register ? It is similar to twitter. You have an account on which you can write messages (like tweets). Other people can like, share, or comment your tweets. In your home feed, you get every tweets of people you are subscribed to, and the tweets they shared, in an chronological order. You have notifications when people answer, share or like your messages. In the "local feed", you get every public message by people on your instance (meaning on the same website as you), and on the federated timeline, you get every message posted on the network that your instance is federated with (it is a bit technical, but no need to understand, in there you have a lot of messages.

You can follow me if you want to have hot leftist takes : @marsxyz@fedi.toniotti.be