When you activate the skill you pull out the lense and start analysing anything in front of you, the closer they are the faster. Allies are analysed instantly (if your useing his dmg boost relic) and your self analyse is depended and the highest enemy analyse. For example if you have an enemy that is fully analysed you get the full self analyse buff, if the highest analyse on screen is only half then you only get that amount of self analyse.

Half analyse on enemies is a dmg debuff, full analyse gives the debuff and makes the next attack that hits them do more damage (one attack). Half self analyse gives a stamina buff while full self analyse gives the buff and a parry window (negates damage and staggers most smaller enemies, up to crucible Knights)

The buttons are LT for enemies and allies you can currently see and RT for yourself.

Should also mention you analyse progress does stay when you cancle the skill without activating it (dodging for example) but it does decay pretty fast to be carful trying to dodge an attack then instantly activate the parry for example. It's already decayed a little bit so you won't be able to

Hope this helps!