First off, welcome to the greatest card collecting site on the planet!
There are a few ways to see others' wants; one is simply clicking a member's ID which on posts appears just under their profile image. Then go to their collection link and depending on if they have multiple collections or just a main collection you should see a Wantlist section. Just click that and you're in!
Adding large volume depends on your setup. If you have sets it's best to just go through the individual set, or if you have it organized by player, then you can access the player pages.
If it's for a Want List or Trade/Sale List, then you will be able to access any set using the appropriate "Add/Update..." links. Then just click the tiny buttons to the left of a card's info, and there's the use of drop-down menus on the set, individual cards, etc. Just explore!
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“Aslan didn't tell Pole what would happen. He only told her what to do. That fellow will be the death of us once he's up, I shouldn't wonder. But that doesn't let us off following the signs.” - Puddleglum in The Silver Chair by C. S. Lewis