You can submit anything that breaks site rules which means there are no limitations whatsoever when creating a post. All kinds of adult content, violence, gore, drugs and etc. are allow to share on the app.
However, there is a variety of "subreddit" that you can find directly from the site that hosts content that breaks rules for other subreddits.
For example, /r/NSFW(not safe for work) contains all kinds of sexual content as well as any other type of inappropriate content as well...