Verbs

A very interesting question: the --ed ending IS one of the signs to tell us that a word is a verb. The tricky thing in English is that some words can belong to more than one "word class" so some verbs can be nouns (and vice versa.)

From the examples you give, we can have "the work" (which would be a noun)

and "the flow" ( which would also be a noun)

We can only decide which way to label a word when we can see what it is "doing" in any particular sentence.

In a way you are looking at it back to front, you do not need to learn a list of verbs and nouns, but if you DO want to label a word as a verb or a noun you have to look at it in context.

You can spot verbs because they often hang around in gangs with pronouns and other verbs:
"to walk" can become
He walks.
He does walk.
He is walking.
He was walking.
He walked.
He had walked.
He had been walking.
He will walk.
He will be walking.

You can spot a noun when it is used with "a or an or the"
or when it has a plural form. (Of course that might be hard to spot, as we use the letter "s" so often in Englsih grammar, and you might mistake a verb ending for a plural)

Shakespeare sometimes used a noun as a verb (even when the rest of the world doesn't) my favourite is in Othello:
when Cassio says he does not want Othello to see him "womaned"
meaning: he doesn't want to be seen with a woman round his neck!