How to flag a book as read

I know that there are fields inside a book for start and finish reading a book. Since I haven't tracked all these informations for my books I would just flag the books I have read.
But how to do it?

You can do this with either tags or collections.

Many people use a 'read' tag or 'read in yyyy'. There is no standard 'Read' collection. (There is one for 'Read but unowned'), but you could create one.