Meaning, if you have a fear of spiders, the Boggart will appear in front of you in the form of a spider. And yes, not as any ordinary itsy bitsy spider.
Your in-house Potter-heads will however not be able to tell you what Boggarts look like. This is because they constantly keep changing form, and no one knows for certain what Boggarts look like.
Yes, they sound very scary, but there are ways you can beat them. For one, you can chant the “riddikulus” charm. This charm will force the Boggart to transform into something amusing and, of course, not scary. However, this method will require a magic wand.
A second option is to have someone with you while facing Boggarts. This will confuse them and they will not be able to decide who to target first. For instance, if you are afraid of cats and your friend is afraid of sharks, the Boggart will turn itself into a cat-shark (half cat, half shark). That isn't really scary is it?
If you wish to be on the safe side and avoid Boggarts entirely, make sure you don't go to dark closed places, as those are a Boggarts' favourite places.
Now that you know everything you need to about Boggarts, fear not if you ever have to face them. However, keep a friend or a magic wand around, just in case!