Would like to point out that, while the summary says this adds lightning resist 1, the picture shows earth resist 1, not lightning. Not really important, as I doubt anybody would seriously use this in the sole hope of taking less damage from a lightning spell (and thus nobody's likely to complain), but just thought I'd point this out.
To get Guild Points, you must first sign up that Guild's GP. You may test at other Guilds, but cannot collected Guild Points at other Guilds, or you will lose your current GP.
Once you've joined, talk to the NPC crafter who signed you up, and once ever 24 hours (real time) they will tell you the item they would like you to turn in. You can craft of buy the item, but you are restricted to how many GP you can collect in one day.
Once you've collected enough GP for your item, you talk the the same NPC and select "I would like to spend my Guild Points" ^^