What is the Difference between SQL and SQL*Plus?
SQL* Plus is a command line tool proprietary to Oracle. You can send SQL queries to the server using the tool. It can also help you format the result of a query.
You should get a good head start on SQL*Plus here http://www.comp.nus.edu.sg/~ooibc/courses/sql/sqlplus.htm
SQL is the query language that is used to communicate with Oracle server to access and modify the data.