Scent glands, responsible for pheromones and a person's scent, are usually on the side of the neck. These scents can sooth, scare, intimidate, etc. - you will typically see a person's scent flare up during times of high excitement (ex. Sex or fights) or if they're scared. Maybe even if they're nervous.

Scents are an easy way to tell who you've been with recently - a person's scent will cling to you if you spend a lot of time with them or touch them. (See the "possessive alpha" trope.)

Scenting, however, takes that idea of a scent and runs with it. Have you ever seen a cat rub its face on your leg? A door? A table leg? They're marking their territory or just telling that table leg, "Hey. I really like you." The same goes for an A/B/O universe - it's a claiming behavior, but not as intimate as a bite. It's not uncommon for good friends to scent each other. Scenting is typically done by touching the jaws or necks together in some sort of delicate fashion. It can also be done by wearing another person's clothes.