In Andrew Marvell's poem, "The Passionate Shepherd to His Love," I find metphors, not similes. (Similes compare dissimilar things using "like" or "as.")
The metaphor compares dissimilar things that share the same characteristics. The poem is comprised of figurative language, so I don't think we need to take all of his descriptions literally.
For instance, in the second stanza, the speaker refers to the birds singing "madrigals" (songs about love) to the shallow rivers' falls. (This is metaphoric, figurative language, as birds don't sing madrigals.) In the third stanza, the speaker refers to a bed of roses. It may be literal, but we often speak of a bed of roses as something desirable, while if we say "this is no bed of roses," we are saying things aren't so great. He may simply be telling his sweetheart that life with him will be wonderful: a metaphor.
Marvell goes on to say that they will weave wool from their sheep and make her dresses from it (unlikely) and place buckles on her shoes of purest gold. And he'll make a belt of straw and buds. Metaphorically, I believe he is saying he will provide all she needs if she will come and live with him. If they love, the gown and shoes will not matter. He compares the things of the natural world to things of the real world: a bed, clothes, etc. He may be comparing the real world to the imaginary world they would create if they lived together surrounding by nature as the shepherds do.
These are the metaphors I found. Hope this helps.
Metaphors are direct equations: Something1 is something2 ("My love is a rose").
Similes are statements of similarity (and weaker than metaphors, generally). They say: Something1 is LIKE something2 (an old form of simile would state "as" instead of "like"). Example: "My love is like a rose." "My love is as a rose."