1) Goto File–>Export
2) The selected project go next,
3) Create new keystore, provide the path for new certificate along with password.
5) Provide the details about the keystore. Maximum year a certificate will be valid is 1000, you can provide any number, alias needs to be given, rest all are easy, country code will be 2 digit.
7) Provide the destination APK path, i.e signed release mode binary will be generated and saved, it will be used to upload to play store
8) Thats all, done. Both signed apk and certificate will be generated in the respective folders.