Learn French: Il est excitant de glisser sur les vagues ! - It is exciting to slide on the waves!

Because this is an impersonal expression. When you use il est (it is) to make a general statement followed by an adjective and an infinitive, the rule is to connect them with de. If the subject referred to a specific noun (like a game or a sport), you would use à, as in Le surf est excitant à regarder (Surfing is exciting to watch).

Could I say C'est excitant instead of Il est excitant?

Yes! C'est excitant de glisser... is actually much more common in everyday spoken French. Il est excitant de... is a bit more formal and is mostly used in writing or careful speech. Notice that both use de before the infinitive when setting up a general statement like this.

Is excitant a false friend for English speakers?

Not exactly, but it is related to a famous trap! The adjective excitant safely means "exciting" when describing things or situations. However, if you describe a person as excité (excited), it can sometimes carry a sexual connotation in French. To say you are excited to do something, it is much safer to say avoir hâte de (to look forward to).

Does glisser usually mean "to surf"?

Glisser literally means "to slide" or "to glide". While the actual sport of surfing is usually called le surf or faire du surf, the phrase glisser sur les vagues (sliding on the waves) is a very common, slightly poetic way to describe riding waves in French.