Welcome to /r/yuri, a place to post and celebrate yuri and shoujo-ai alike. Follow the rules of the subreddit, along with reddit's general rules and you should be good to go!
What is Rule34? Simple. "If it exists there is porn of it. No exceptions." This is an adult only subreddit. You must be over the age of 18 or whatever age limit your local law deems fit to view adult content.