For writing assignments in school and, especially, for college application essays, it is critical to avoid grammar and usage mistakes. Unfortunately, we are all prone to making them. However, there are some great resources available. I subscribe to the Chicago Manual of Style online. It’s not free, but it is comprehensive and invaluable (IMO).
For a free resource, the folks at Grammarly have a blog that can be useful and they have a bit of fun with words and usage now and again. Here is one example that I found interesting: https://www.grammarly.com/blog
Today I ran across another excellent post, so it pays to check the site frequently. By the way, I don’t have any relationship with Grammarly that prompted these comments.