You don't HAVE to post. Failing to do 30 contributory posts in a given month doesn't mean you can't do it again next month. But you do need to post 30+ contributory post in a given month to request the Posting Bonus for that month.
Since you just joined, consider the first couple of days on the site as educational and start your posting process (for the bonus) for the month of May.
Click on the link, PAID TO POST, at the top of any Forum page and read through the bonus requirements. In the middle of that page, in green, is another link that takes you to the page where you complete the request for the bonus.
On the right side of that page is a link that allows you to see all of the posts you've made. Right above that link is a number indicating how many eligible posts you've made so far this month. (Posts to the Contest and Promotion section are considered not eligible.)
I noticed that you have 30 posts under your name. If they were all completed in April, you are eligible to request the Posting bonus. When you review them make sure they meet the contributory guidelines in your own mind. Then select the best 3 (the ID number is at the top of the post) that you want to use to make the request.
If you made you submission yesterday (April 30th), you can expect to receive the bonus (if all posts meet the contributory guidelines) by the end of May. If you made the submission today (May 1), it may take until June 30 to receive the bonus. At the bottom of the submission page is a history of your posting bonus requests. It will give you a time frame on how long you will need to wait until you receive the bonus.
I usually have more than 40 eligible posts before I request a bonus, just in case some of the eligible posts don't meet the contirbutory guidelines. Very easy to do -- in fact, it becomes addictive after a while.