Pl post a link to what exactly you have downloaded - pl also post your OS details. With a typical install, you can use the command-line interface to interact with the database. Other option is to use a GUI interface like SQL Developer (Oracle SQL Developer Downloads</title><meta name="Title" content="Oracle SQL Developer Downloads…)
Documentation for all of these is available at Oracle Documentation
I have downloaded oracle database
And did you install it ? Do you have a database ? Assuming you're speaking of XE database, what's your OS ?
Please explain in detail what you've done.