When Iran setup their blockade in the Straight of Hormuz, what exactly was it intended to block? Which countries were being denied access? For example was it intended to block both import and exports between US allies, but all other trade was allowed? Did Iran's blockade hurt their own economy, and if so, why did they do it?

How is the US's imposed blockade different than Iran's? Is it so that Iran can no longer export and do business with it's allies (which presumably was still happening when it was just the first blockade)?

It seems like most countries' economies are being damaged by the blockades and none are benefiting from it. What are the objectives, to pressure the other side into agreeing to demands?