I was trying to update my Mac to Mojave but when it was restarting it got stuck and all I see is apple logo. I am not sure what happened and how can I get back to start m Mac. Any help please.
This is what I see in photo below.
I assume that you didn't shut the lid down while updating it or basically didn't put it to sleep through anyway.
if you didn't, I just recommend waiting.
if still stuck, try reinstalling using recovery mode. which is holding CMD-R just after power up during restart . Apple support for reference