Edit : Can anyone tell me which is best server for Matrix ?

element.io is a server so that doesn't sound right.

Do you mean Matrix-Server?
You can have a look here:
https://joinmatrix.org/servers/

... or host your own server.

If you have a certain community in mind, maybe just join their server.

Some infos to get started:
Matrix is the chat-protocol, so the language, that server and client talk to each other.
Element is one of the many clients, so the Software of the app/website that you use to send your messages to the server.
Thing with matrix is, that the servers are mostly federated like Lemmy, so you can chat with all other users and join all other communities.

If you want to know more, you can ask me or read here.