Now you'll need to pick what "permissions" you want the key to have.
Remember that the GW2 API is read-only (you can't change anything
on a GW2 account), so don't worry about giving the key too much
information. In any case, the key's stored locally (on your computer),
so no one but you can see it!
You have to pick "account", as that's a sort of "base" permission.
You'll also need "characters", "builds" and "inventories".
Click CREATE API KEY once you're happy with your choices.
Copy that API key down somewhere
Using Guild Wars 2 Trinket Manager
This tool is designed to help you keep track of (preferably ascended) trinkets on your
account. Once you provide an API key, it'll automatically retrieve and list all your
characters on that account.
Each character will get a single row in the table.
You'll also have a Pick Stat button on the far-right for each character. This is
allows you to select your target stat.
For example, if you've selected "Power" as a target, trinkets with
Berserker's, Valkyrie's, and Marauder's will be acceptable, whereas
Sinister and Carrion will not (they're Condition stats).
Your "goal" is, after picking a target stat, to fill each of the boxes with an
appropriate-stat, ascended trinket.
To examine each trinket, click the manage button.
This will also give you options to replace the trinket.
You can optionally hide any characters that are "finished" (i.e., all trinkets are ascended or legendary, and are of the appropriate stat type), you can optionally hide those characters.
You can also hide any characters that are not yet level 80, since they obviously cannot equip ascended/legendary trinkets.
(You'll be given the option of picking a specific stat below, if
you want)
Stat:
Category "All" isn't a
valid category (it's basically every stat option), so you'll need to pick a
specific category below!
Category "Not Recommended"
contains stat combinations which I'd personally not recommend you use. Usually,
they're too middle-of-the-road to be useful.