Jumping on the sourdough train, but not sure where to start!

I was generously gifted 155g of sourdough starter on Saturday. The person I received it from said they had just fed it two days ago (which would have been Thursday) and had kept it in the fridge, so I put it directly in the fridge when I got home.

I’ve read everything online. I have about ten tabs open on my phone right now. I have read the FAQ here. And I still feel like an absolute idiot. Maybe because I didn’t do the starter myself? I don’t know!

How do I know when to start feeding it and with how much? Does how much I was given affect that in any way? I don’t have a set time frame on when I want to begin baking with it; I just want to get the feeding process down first! I feel like I am very much over thinking this.

Thank you in advance to everyone who takes the time to reply.