Work with SQL*Plus through command prompt windows

Dear All,

I have big problems trying to access a database using SQL*Plus through
command prompt. I am a beginner DBA, and my first challenge is to make
a backup and recovery of an Oracle9i database.
I tried to access through SQL*Plus windows but it showed me "TSNames
No listener"...and accessing using SQL*Plus through command prompt I
could, but now...I can do anything else, I can't use RMAN, V$ .... I
got completely lost..and I will appreciate so much any help.

Thanks in advance for your time.

Bets regards,
BeginnerDBA