Unity Editor keeps crashing without warning and I don't know why

I’m new to Unity and don’t know much about how it works. I’m trying to do the online course Game Design and Development 3: 3D Shooter on Coursera, so I’m using the assets downloaded from the lesson. Unity Editor has suddenly started to crash after a few seconds of opening my project and I don’t know why. Can someone please help me with this?
And please give me instructions like I’m a five-year-old as I really am new to Unity.
Thanks in advance :slight_smile: