To see your Membership Subscription options, you can go to your profile page by clicking on the Profile Icon > My Profile and click on the Edit Profile button.
At the bottom of your profile editing page, you will see the panel with Membership Subscription settings. With the toggle-bar, you can activate any or all of the weekly, monthly, annual or lifetime options and set a price.
After confirming your preferences, the option to publish your content as members-only will be active on the article creation screen.