To sell membership in the store, create a package type with membership included, and then create a store listing for that package type.
There are many ways to organize your memberships and package combinations, depending on your billing practices.
Sell membership separately
The most flexible option is to sell membership separately in its own package. You could even offer multiple membership packages – for example a monthly membership and a yearly membership. Members will buy this package once, and then buy other packages as needed.
Create the other packages that you need without membership. However, for packages that are intended for members, you should enable the Require membership option in the store listing. This will enforce the membership requirement in order to use the package. Customers who do not have an active membership will not be able to use purchased packages until they buy the membership package or a manager adds membership to their account.
Sell membership bundled
If members buy exactly one package per month, and you only offer membership on a monthly basis, then you can directly include membership in your packages. This way, customers will buy their lessons, classes, and membership in one package.
There might be some packages that do not have membership included. For example, a trial package, such as 2 introductory lessons for non-members, would not have a membership included. Similarly, a package of 10 à la carte lessons would not include membership, since presumably this package would be in addition to a regular monthly package which does include membership.