These bracers can absorb a spell that is being targeted at you. You can use a reaction and a arcana check, if successful the spell not only doesn't effect you, the bracers absorb the spell to be used later. You can use the spell anytime but no matter the spell it will need to be a somatic cast. You can't absorb another spell until you use the spell already in the bracers.

The arcana check will change by the spell:

cantrip = > 1

1st = > 3

2nd = > 5

3rd = > 7

4th = > 9

5th = > 11

6th = > 13

7th = > 15

8th = > 17

9th = > 19

If you remove the bracers the spell in the bracers will be deleted, how ever if the bracers are removed unwillingly you have a hour before the spell is removed. If you didn't already know what the spell was before you absorbed it then you still don't know until you cast it.