You can register yourself on multiple Instances and try yo see the difference between them.
Anyway, after some exolorations, most of tbe people prefer to stay on one single Instance that they will choose as their base (it's somehow like trying different telephone companies and then choosing one, but with the difference that in this case an Instance is not only a service provider but also a community made of people, with his own culture and rules).
If you want to change Instance is possible to transfer to the new one all your contacts and followers. This is only available if both the new and the old Instance run the latest version of Mastodon's software