Hi, see the ratel docs here: https://dgraph.io/docs/ratel/overview/
Using https://play.dgraph.io is just like running a local ratel, so you should just be interested in the connection settings. For instance, connections to a local environment would be to use the server connection box as http://127.0.0.1:8080. (the scheme is important to put in)
No password or anything like that is necessary unless you have specifically enabled ACLs (an enterprise feature)