How to use has_many :through association??

Let's say I have

group has_many :memberships has_many :members, :through => memberships

and vice versa, and there's a model called memberships that stores extra information, such as the reason for joining, etc.

How do I then actually USE this in my models, controllers and views?

Do I need to create new memberships using a form?

Can I for instance, on a group's show view that displays an individual group, have a form at the bottom that allows the CURRENT USER to JOIN the group and provide a reason for joining by sending a put request form to the memberships controller? How would I access the memberships form if I'm on the group's page?

Thank you for your help and patience.

I can't get what you exactly need but I am prefered to refer this link