The dot product (also sometimes called the scalar product) is a mathematical operation that can be performed on any two vectors with the same number of elements. The result of the dot product operation will be single scalar values that is equal to the magnitude of the first vector, times the magnitude of the second vector, times the cosine of the angle between the two vectors (at least for 2 and 3 dimensional vectors).
If the second vector in the dot product operation is a unit vector (thus having a magnitude of 1), the dot product will represent the magnitude of the first vector in the direction of the unit vector.
As an alternative to the above method of calculating the dot product, you can also break each vector down into components take the sum of each set of components multiplied together as shown in the equation below. Either of these two methods will yield the same result.
Finally, as with all vector operations, we can use computer tools such as the dot command in MATLAB or the Wolfram Vector Operation Calculator tool linked to in the left panel.