Question

i don't understand the thumb rule

Answer 1

Thumb rule shows direction of magnetic field and current direction or force

Answer 2

Thumb Rule Helps to know the direction of the magnetic field with respect to the direction of the current flowing through the conductor. If you imagine holding the straight conductor in your hand such that the direction of your thumb point the direction of the current, then the curls of fingers around the conductor will the direction of the magnetic field.

Note: The Thumb should be perpendicular to the curl of the fingers.