If you do not increase your pump load, then not a lot will happen to the visible body. There are no calories in steroids, so you will not become fat!!!!
However, you blood pressure may go up and your natural testostorone levels may be altered. That means if you are a bird you nipples can become hairy and you stop your monthlies. For men, hair falls out and the dinky shrinks.
They really are not advisable unless you are a competition body builder. They do not make you bigger or stronger, they just increase your appetite to pump iron.