Oracle database program runs but does not execute query

For my university course,i had to install oracle database program both in my laptop and computer. But when i installed the 10g enterprise edition, it was not only installed properly and also i could open it.
But when i tried to write some query for practicing using my desktop, the oracle database program did not execute it which means i can only run the program, but can not execute it.

I need help for this.
