With double D rings one passes through the other if the rings are on each strap (mine is like that - Seago), if both on one strap the loose strap end would pass through the first ring, around the second ring and back through the first (been used on crash helmets for years).
Check dates on activators and check for green dot on hammar avtivators, inflate overnight to leak check but use a pump not your breath as that fills the bladder full of moisture and rots the gas bottle.
If in doubt have them properly serviced before relying on them.