It just allows us to use the noun phrase as an adjective to describe learning how to concentrate. Of value means valuable. "It" is a false subject -- we could say "learning how to concentrate is extremely valuable."

Yes, but that part is usually 100%! We use "of" with nouns to mean that we think or feel a certain way about them. We could (and should!) use the verb or adjective forms of these nouns as well to mean the same thing, e.g.: This item is of concern to us (We're concerned about this item) This product is of interest to us (We're interested in this product) It is of the utmost value to learn how to concentrate (It's extremely valuable to learn how to concentrate)

Thank you so much for your comment, Tony.

"of" indicates possession. The book of John = the book belongs to John. It is "of the utmost value" means that it possess the utmost value.