If you have a toilet brush, the trick is knowing how to clean it afterwards. The using part is pretty simple. Just scrub. I'm not going to get more detailed than that. That's OK, isn't it? I think were all on the same page there.
But for the cleaning…here's a good tip! After you've brushed, hold the toilet brush where the water comes out. Then flush, letting the falling water rinse your toilet brush. Then go ahead and store it.
Get a little cleaning boost with Duck® Deep Action Gel liquid cleaner. That'll do the job.