What's the point of (something)?

"The point" of something is the reason for doing it. But this word is often used in the negative sense: "what's the point?", "there's no point", "I don't see the point", etc.

You can say "What's the point of (something)?" or "What's the point of (doing something)?":

What's the point of Facebook? I don't get it.

What's the point of studying math in school anyway? No one ever uses it in real life.

When you ask "what's the point of ___?" it's usually a criticism and can sound negative. So you should use it when you are angry and annoyed about something. Depending on your personality, you may not want to show people that you're angry unless you're close to them. A more polite way to ask "What's the point of this meeting?" would be:

"What's this meeting about?"

wear a helmet

A "helmet" is something hard that you wear on your head in order to protect it. People wear helmets while riding motorcycles or bicycles and when playing certain dangerous sports like baseball or American football.

buckle (a belt or strap)

A "buckle" is the part of a belt or strap where you attach the two ends to each other. The belts people wear on their pants have buckles. So do some shoes, straps for handbags and luggage, and seatbelts.

When you attach something with a buckle, you're "buckling" it. You "buckle" the strap or belt itself:

Can you buckle that strap?

And you "buckle up" or "buckle in" the thing that's contained by the belt or strap:

There you go; you're all buckled in!