How does the steering lock function work on motorcycles

There is a hole in the steering neck of the frame.
When you turn the switch to ''lock a stud moves out of the switch and fits into the hole.
Just like a ''dead bolt'' on a door.
The forks have to be turned to a specific position, to line up the stud with the hole.

If your ninja 250 is the same as mine, you have to have the handlebars turned all the way to the left and push the key down a little in order to turn it left to the lock position.

Do not rely on them, they are easy to defeat and, in the unlikely event that it defeats the thief, the leverage applied will damage your headstock. It is difficult to believe that motorcycle manufacturers cannot come up with better security measures than this, do not let me get started on helmet locks.