Hello, how do you see a list of users that have things you need?

as far as I know you can only do it by individual cards:
Go into card database
type the card in your looking for
then it will come up with a list of users that have that card in their tradelist

If you join one of the communities then you will see matches of people that have things that you are looking for as well as the reverse. The most common community is the reddit one, which you can join here:

http://deckbox.org/communities/reddit_mtg_trades

and you can see the list of all communities here:

http://deckbox.org/communities

Thanks!!