How to config 'registrar' in default.json of condenser

In default.json, there is a section named: registrar

"registrar": {
"account": "initminer",
"fee": "50.000 TESTS",
"delegation": "1000000.000000 VESTS",
"signing_key": "xxxx"
},

How should I config values of account/fee/delegation/signing_key?
And what is the meanings of each field?