A lot of these questions have been answered in detail in the item’s thread, so I’ll be brief here. (Check out the full thread for those details.)
CORRECTION: You use the sigil to put this field on any solid object. Object suggestions are in that linked thread.
No, it does not have to be visible.
It’s best not to use a “garment” as those wear down easily or otherwise have shorter lives than something more solid, like a necklace, ring, etc.
You place your object (that you want to have the field on) on your printed sigil.
You say the keyword that’s printed underneath your sigil (which it will be if you got your sigil through Patreon).
Then leave your object on the sigil where it will be undisturbed for 3 hours.
After that, all you need to do is carry your object with its field.
Store your sigil away for later use.
Carry/wear your object whenever you want those qualities that this field imparts.
When you don’t want those effects, take your object off.
Edited.for corrections.