There is something invalid about the OraDBHome1 client. That's why it's red. you can click the '...' button next to it for details.
If you click the "Connect Using" dropdown, is there one listed that is not red?
If so, choose it. Then enter username and password. Then select the database in the "database" dropdown. Then click "Connect".
If that's your only installed Oracle client, you'll have to figure out why it's red, then fix that.