The constriction rings are only if you want sex, i.e. to retain an erection after taking the tube off.
For penile rehab, you don't use them.
For the clear silicone rings, when new, stretch it first (like you would a balloon before blowing it up), and maybe heat it in warm water. Not necessary if it's been used before. Don't use the loading cone which comes with the pump with these rings, as it can cause micro scratches on them, which will cause them to snap. (They tend to last up to 40 uses before they snap anyway.) Just stretch over the open end of the pump tube.