Yes you are right.
A logged-in site visitor selects a membership plan by clicking the plan or a button. (If the visitor is not logged-in, the sign up page is displayed.)
This way you have full control over all of your members and you can always limit your members only pages to certain users on different paid plans.
https://support.wix.com/en/article/limiting-site-pages-to-paying-members-using-the-paid-plans
You can obviously just keep the free info on pages that are open to all users and so keep your free content open to all, whilst keeping the member info behind the paid plan pages.
However doing it through Wix Paid Plans app gives the user the opportunity to sign up as a site member and then let them either do a trial plan to test your site or to choose the specific plan that they require, or you can create a free plan that they can be on until they cancel the plan or upgrade to a new plan to access content that can’t be viewed under the free plan.