Free membership site

I would like a new visitor to register on the site with minimum effort (ideally by just entering email address) and stay on the site to view the member only parts of the site.

Does a user always have to leave the site to click on an activation email in order to register with a membership site?

I hope to set up a site with WordPress where people can access member-only areas of the site by only entering an email address.

no its not.

Thank you Dmitry