Importing into Oracle

I need to export from user 'A' in a production database and import to a user 'B' in a development database with a different tablespace. Do you have very detailed step-by-step procedure?

This is a pretty common procedure, which isn't too hard to accomplish. So here is a step-by-step guide.
Export the entire schema from production:
exp userid=system file=user_a.dmp log=user_a.log owner=a

FTP the dump file (in BINARY mode) to the development server.
Make sure user B exists in your development instance.

Run this command:
imp userid=system file=user_a.dmp log=imp.log fromuser=a touser=b

The only big sticking point is that user B may have a different default tablespace than user A, if user A exists. If this is the case, and user B has been granted the CONNECT role, then user B's tables will be created in user A's default tablespace. To stop this, make sure that user B has the correct default tablespace and make sure that you revoke UNLIMITED TABLESPACE from user B.