Can i advertise my shop here?

Read the FAQ & guidelines:
https://www.steamgifts.com/about/faq
https://www.steamgifts.com/about/guidelines

What do you mean by "sell my steam games"?

If "my games" means that you have made a steam game you can 1) advertise it either in giveaways or 2) there is a 'game showcase' category with the following rules;

"You are invited to share your Steam game in this category when you are a game developer. You can show us your work-in-progress, let us know when your game launches on Steam, or poll our community for feedback. We encourage you to provide additional information about the game, such as a description, what you are trying to achieve, why we may find it interesting, or how your game differs from others in the same genre. You are limited to one open discussion per game. Be considerate to not repeatedly bump your content if the community is not engaging with your post."

If "my games" means you have bought some keys and are reselling them. Reselling keys or linking to key reselling sites is not allowed anywhere on this site.