How do I make a Macintosh startup disk?

Hi, I’m new to Macs, and I think I need a Macintosh startup disk… I have a powermac 7200 that was donated to me. When I power it up,there is an icon of a blinking disk w/a question mark on it… and that’s as far as it goes.
If anyone can help me i’d appreciate it!

Thanks!
Sherry