Snapchat is a valuable social media app for people who don’t mind sending their friends embarrasing photos.

 (LIONEL BONAVENTURE/AFP/GETTY IMAGES)

This is not your grandkids’ Snapchat.

The Social Media App that’s popular with the youngest Millennials is now booming with older people: Now 38% of people ages 25 to 34 use the flighty picture-sharing app, according to an online report — a 100% increase from just two years ago. And 14% of people over 35 use the app, too — which represents a 35% jump.

At this point, the only adults not using Snapchat are the ones who don’t get it. So let this bona fide Millennial — I’m 18 — explain it to you old folks:

The first question: What is Snapchat?

Snapchat allows users to share photos and videos with friends. Snaps — messages between users — are viewable for up to 10 seconds from when first clicked. After that, they disappear. Most snaps are selfies accompanied by a line of text to capture the mood. And unlike other social media apps, Snapchat allows users to pick whether to send the photo to one, multiple or all his connected friends.

Who uses Snapchat?

Almost everyone under 24 uses it. And many celebrities and political figures use Snapchat to give viewers a seemingly “inside” look at their lives (don’t believe it). You can follow Hillary Clinton on the campaign trail, go behind the scenes with Jimmy Fallon or Calvin Harris, or watch clips from the White House — all in the form of longer “stories” that last for 24 hours.

Chrissy Teigen also captures her longer moments in a Snapchat “story.”

(SNAPCHAT)

How is Snapchat different all the other forms of social media?

Snaps disappear once viewed — leaving nothing embarrassing for future employers or future lovers to find. Snapchat is also more casual and conversational. Snaps are rapidly sent back and forth between friends. Instagram posts tend to be carefully curated to put its users in the best light (sometimes literally). And Facebook can become overwhelming from the sheer volume of photos and political posts in your feed — and the feeds of people who tag you.

Snapchat and Twitter are similar in that they allow users to provide “in the moment,” often humorous, updates. But Snapchat is much more visual and personal because you can send a snap to a single person rather than all your followers.

Also, on Snapchat, users can see when their friends have viewed their snaps, as opposed to other media, where users know only if their photo or post has been “liked.”

What is Snapchat best for?

Snapchat makes it easier to let loose and relieves users of worrying about every little post. Snapchat is basically “shoot first and never have to answer questions later.” Your embarrassing moment, small frustration, or amusing encounter is effectively communicated to a few friends in an instant with a simple picture — and then it’s gone.

(VIA SNAPCHAT)(SNAPCHAT)

What better way to cement a friendship than posting a Snapchat selfie, as Blac Chyna and Kylie Jenner did in April (left). And Calvin Harris used the medium in May.

How is Snapchat evolving as a form of real media?

For now, most users treat Snapchat as something fun and frivolous, but the app has recently expanded its “live stories” feature to allow longer — and longer lasting - clips. That’s where Snapchat curates footage from live events such as Jose Reyes’ return to the Mets on Tuesday night. Anyone in these locations can contribute to these live stories.