Depends on why you can't make it. If it's in a few days, it's most likely your responsibility.

it’s your responsibility. i would ask other shifts if they want your shift and if none of them want it, ask the manger for the other stores that are in your district and ask is someone wants to be a borrowed partner

A few days from now, it's your responsibility. Is it a key shift or a coverage? You're probably going to get in significantly more trouble if they have to change operational hours if you don't come in. But if you're coverage and it makes them down a person, it's the same as any other call out. My store usually gives a verbal warning, making sure you understand policy before writing people up.

Depends on the situation. My manager printed out the official call off/coverage policy a couple months ago (granted, it could have changed). If you know ahead of time that you can’t make a shift it’s your responsibility to find coverage. But if the shift is today and you’re calling off because you’re sick or have an emergency, it’s your managers responsibility

If you have the Starbucks Partner Hours App you could “Offer Shift” for that day which lets everyone in the district who has the app that you are looking for coverage.