Torque

Torque is a measure of "twisting force".
Power is a measure of twisting force x speed.

Torque is usually expressed as a Force x a distance So for the same Torque if you double the distance you halve the force to get the same answer.

So kg.cm is kg force x centimetre distance.
In fact kg are a mass and not a force BUT kg are sloppily used as a force in many cases.

In your case 3 kg.cm means that a "force" of 3 kg acting at a radius of 1 cm would produce the same amount of torque as your motor.
Equally that could be 0.1 kg x 30 cm, or 10 kg x 0.3 cm or ...

A motor with 1 kg.cm torque is capable of holding a 1 kg weight at a radial distance of 1 cm.

Here is a diagram to explain.

Torque is the cross-product of force and distance: F=τ×d$F=\tau \times d$. So the same weight, at twice the radial distance, will require double the torque.

Note that the measurement 'kgcm' is 'kilograms-force × centimetres' and would be clearer if written as kgF.cm$k{g}_F.cm$, which avoids confusion between kg (mass) and kgF$k{g}_F$(force.)