When you find your own pattern from a book or a site, the next step is to get the required yarn. You can sometimes order it online, but the best way to get what you need is to go
to your local craft store. My favorite is Michaels. That takes time and planning. You also run the risk of them not having what you’re looking for, so then you have to make another plan. Crochet kits handle all that for you. The yarn required ships with the kit, meaning no time wasted going to the store, and no worries if you won’t have enough. From my experience, the kits include more than enough yarn to complete them. This is good if you make mistakes.