Oracle 10g SQL加上未知的用户名，密码和主机字符串

I have just installed Oracle 10g database and also oracle developer suit, which is installed as DevSuiteHome1 in my computer. I could not use SQL plus because I dont know the exact username, password and host string to connect. During installation I did not ask to enter any username & password. Then what would be the username,password + host string? Help me out of this.I have just installed Oracle 10g database and a