Do I have to make another VM instance to run another app? Or can I run multiple apps in one instance?

>Solution :

Straight forward answer – YES

VMs behave similar to what a regular physical machine would.
In any machine you can run multiple apps , just that they would need to run on different ports.
So, you can run multiple services / applications in a single VM but they would need to run on different ports.

The other things you might have to consider is like the capacity of the VM. Running multiple services in parallel will only lead to more consumption of the RAM and CPU and might lead to exhaustion of the complete capacity.