Could you help me to understand the timer interrupt

I am trying to understand how timer interrupts work in a microcontroller. I want to understand how the timer interrupt works in any microcontroller Before to understand how a timer interrupt works in a particular microcontroller,

I am assuming there is a timer that starts from 0, 1, 2, 3 . . and ends up to 255. I want the timer interrupt to be generated when timer reaches at 30

1. When the timer interrupt generates, will the timer increment beyond 30 (30, 31, 32, ... 255)...

Could you help me to understand the timer interrupt