i have installed toad for oracle (the latest version) , but it can not see my db ? why ?
what should i do ?
You need to install an Oracle client, you need to configure a TNSNAMES.ora file for that Oracle client, and other Oracle prereq’s. My book on intro to Oracle and Toad Handbook cover such topics. These are newbie Oracle questions - so not unusual to ask 
i already have an oracle client ,
how should i configure the tnsnames.org ?
it’s not a problem of configuring , it always see the database without doing anything ,
i found the problem , it was that “connect using” was not set to my database .