Std testing

How do doctors test you for STDs? I know that may be a stupid question but I'm curious because I want to get tested but I'm kind of nervous.

And about the posting multiple times, I didn't mean to do that...it said the post failed so I kept trying and then I ended up deleting it and rewriting it. I didn't realize all my attempts went through because each time I tried to post, like I said, it told me it couldn't go through. I deleted all the other posts about it. I'm sorry but we all know how the internet can be...mistakes happen.