I am having trouble with my Mac. When I turn it on it says support.Apple.com/Mac/startup?

Hello!

A folder with a flashing question mark means that your startup disk is no longer available or doesn't contain a working Mac operating system.

From If your Mac starts up to a question mark - Apple Support,

If the question mark is persistent, and your Mac does not start up normally:

1 - Press and hold the power button on your Mac for up to 10 seconds, until your Mac turns off.

Every Mac has a power button. On notebook computers that have Touch ID, press and hold Touch ID.

2 - Use Disk Utility to repair your startup disk. Follow the steps for a Mac with an Intel processor.

3 - If Disk Utility found no errors or repaired all errors, reinstall macOS.

4 - If you still need help, please contact Apple Support.

Jack

Enter the address into a browser on another computer and follow the instructions.