Torque (also called moment — mostly by engineers) is calculated by multiplying force and distance. The SI units of torque are newton-meters, or N*m (even though these units are the same as Joules, torque isn't work or energy, so should just be newton-meters).
In calculations, torque is represented by the Greek letter tau: τ.
Torque is a vector quantity, meaning it has both a direction and a magnitude. This is honestly one of the trickiest parts of working with torque because it is calculated using a vector product, which means you have to apply the right-hand rule. In this case, take your right hand and curl the fingers of your hand in the direction of rotation caused by the force. The thumb of your right hand now points in the direction of the torque vector. (This can occasionally feel slightly silly, as you're holding your hand up and pantomiming in order to figure out the result of a mathematical equation, but it's the best way to visualize the direction of the vector.)
The vector formula that yields the torque vector τ is:
τ = r × F.