When do you use dynamic memory?

Question

I just don't get why and when you need it.

Answer 1

One uses dynamic memory, if one does not know how much memory is required at runtime of the program.
Typically this is due to user input (keyboard input on the machine, input via network or configuration files etc.)

Answer 2

using dynamic memory is tricky and challenging
if you are new avoid using dynamic memory
it can be hard to manage