There is no separate invitation feature, and you do not need one. A person becomes a member the moment they exist in your platform with something to reach, and MemberArea takes care of telling them. Which door they come through depends on how you got their name.
By hand, one or a few at a time
Open the member list and click Add. The form asks for name, email and the language they should see, then for the access they get, then shows a review.
The switch Send credentials by email on the review step is the invitation. Leave it on and every person in the batch receives an email with a link to set their own password. Turn it off when you want to tell them yourself, for example inside a call or a workshop.
This is the right door for a colleague, a customer who paid you offline, a test account or the first handful of people in a new platform.
From a list
For more than a handful, import a CSV. The import maps your columns to member fields, checks every email against the platform and assigns access to the whole list in one go. Whether the imported people get an email is a switch in the import, the same as in the form.
Through a purchase
When someone buys a course, a membership or a ticket in your checkout, the account is created for them and the access that belongs to the product is assigned at the same moment. The order confirmation carries their login. Nothing for you to do, which is the point of selling through the platform.
What they receive
The credentials email comes from your platform, in the member's language, with your logo and colours. It contains one link that lets the person choose a password. The link is personal and expires, so someone who waits a week uses Forgot password on your login page instead, which sends a fresh one.
Not sure whether an email arrived? Open the member's profile and trigger the password reset from there. It is faster than debugging mail delivery for one person.
Where they land
After the first login a member sees the dashboard and everything you assigned. Groups are the easiest way to keep that tidy: put the person in a group and the group carries the courses, hubs, forums and calendars with it, now and whenever you add something to the group later.