For starters, you’ll need a good overview of exactly what a modifier is and how it’s supposed to work in a sentence. This explanation from Grammar Bites can give you a good outline, as well as a few useful examples to begin with. We’re used to thinking about modifiers as problems in a sentence, but in fact they can be very useful. Grammar Monster shows you all the ways modifiers can be used to add information to a sentence, and gives you a chance to test your own knowledge with a few practice sentences.

Now that you’ve got the basics, you might want to learn more about the different problems that modifiers can create when they’re improperly used. Grammar Monster explains dangling and squinting modifiers, and also the problem of misplaced modifiers overall, and how to identify the different types. Grammar Girl gives a very detailed guide to the problems that can arise when modifiers are misplaced—with some funny example sentences, too.

To give you a sense of the many shapes and forms that modifiers can take, you could read some more example sentences on Purdue University’s grammar guide, or take a look at this source, which has a long list of example sentences that you can use to test out your new-found knowledge.

Once you’re done learning about modifiers, why not watch a few more of TED Ed’s grammar videos?