Welcome to AAC!
Please post your best effort at describing the circuit operation, so that we can guide you where necessary. This forum is for 'Homework help', not 'Homework done for you'.

 

Her you will find some information about your circuit:
https://forum.allaboutcircuits.com/threads/monostable-multivibrator-help.70000/#post-486225

 

Welcome to AAC!
Please post your best effort at describing the circuit operation, so that we can guide you where necessary. This forum is for 'Homework help', not 'Homework done for you'.

This is what I have, but I think it is not right or it is incomplete (sorry if it is not well understood, I translated it from Spanish to English with the translator).
When pressing the pushbutton the circuit is triggered, the capacitor starts to charge through R1 and the NOR gate U2A is activated, it is working as a NOT gate and as the DC capacitor works as an open circuit, the NOR gate U2A would still be NOT, therefore it would have 0V at the output and the led would not light up.

 

Ah, I took the image of the circuit with the key closed, I got confused, the circuit is tested and described with the key open.

 

Thus

 

What happens at Input to U1A when you close the switch?

 

What happens at Input to U1A when you close the switch?

Do I get a 0?

 

Study the current flow in the capacitor C1 when you close the switch. Follow it to the U1A input .

 

Is the capacitor discharged?

 

Consider the two situations:
1) It is charged already,
2) It is discharged