I've just installed and started MongoDB from official docs: https://docs.mongodb.com/manual/tutorial/install-mongodb-on-os-x/.
brew tap mongodb/brew
brew install mongodb-community@4.2
brew services start mongodb-community@4.2
How can I get URL / Connectionstring for the server?
Your fresh standalone installation probably has no access control configured yet. So the connection string is:
mongodb://localhost:27017
Otherwise, you have to provide username, password and auth source database in the connection string, e.g.
mongodb://username:password@localhost:27017/?authSource=admin
Continuing from the same steps on the installation docs, there is a section for Connect and Use MongoDB, for connecting to the database from the shell.
$ mongo
MongoDB shell version v4.4.3
connecting to: mongodb://127.0.0.1:27017/?compressors=disabled&gssapiServiceName=mongodb
Implicit session: session { "id" : UUID("....") }
MongoDB server version: 4.4.3
...
It should show the connection string it used (you can disregard the rest of the string after ? unless it is authSource):
connecting to: mongodb://127.0.0.1:27017
If you are already connected via shell/terminal, use db.getMongo() to return the connection string in the shell/terminal.