I have submitted a story and its been returned because of bad grammar can anybody help me ?
Grammarly and spellcheck are helpful to an extent.
Depending what country you're from, comma rules vary, but here's some links for punctuation rules
https://www.skillsyouneed.com/write/punctuation1.html
https://www.thepunctuationguide.com/ (American, but has a page for British and American differences in standard punctuation)
You can also look into literary devices. You don't need to know what they're called, but it's always good to have many tools at your disposal to express yourself, even if you're mostly expressing how horny you are. https://www.masterclass.com/articles/22-essential-literary-devices
Hope those help.