Do you know any website I can use to improve grammar and writing?

Hi, I want to know if anyone knows of a free website that has grammar games and that nature to help improve writing skills and grammar. I am yet to get a 100 on any essay I have written because I make the same grammatical mistakes, as well as fail to properly proof-read the essays. I have a hard time recognizing errors because I do not know the rules. I also have a hard time memorizing rules because I usually want more examples.

Thank you for taking the time to read this and I hope there is something good out there that I can use with your help.