"Attendance" is a noun that means "showing up for something". You use "attendance" to talk about people coming to a meeting, a class, a party, and so on:

Comic-Con's attendance last year was estimated at 130,000.

Their school has a strict attendance policy.

The verb form of this word is "attend (something)":

I'm sorry, but I won't be able to attend today's meeting.

"Attendance" is used in formal communication for business or school, or when you're talking in an analytical way about the number of people who came to something. In a more casual situation, you can use the word "turnout" to talk about the number of people who came.