If you're a monthly creator, "paid posts" do not apply to you, as your patrons will automatically be charged on the 1st of every month.
If you're a creator charging "per post", you need to make sure that you select which posts you want to charge your patrons for. As shown below from the make a post modal, you will see a check box where you can select to charge your patrons.
If choose to charge your patrons, remember they won't be charged until the 1st of next month! Also, you should know that you can't charge specific patrons while not charging others. Your patrons can find these posts in your Overview and Posts sections, regardless of whether you decide to charge your patrons or make a free post.
Learn more about tagging, scheduling and attaching content to posts here.
note: if you are making a paid post ALL of your patrons will be billed- so you cannot select specific tiers for the post itself, if you have a reward that you want to go to just one group, you can make a free post with the content, and set it to the appropriate level.