Vector addition is the process of summing vectors. It is analagous to adding together more than one matrix, each having one and only one row. To accomplish this, one must add corresponding individual corresponding components, placing the results in a new vector. For example, to add <a, b, c, d> to <a, f, g, h>, you add a to e, b to f, etc. and obtain <a+e, b+f, c+g, d+h>
as your resultant vector.
If you are unfamiliar with this mathematical notation of vectors, consult the "vector" node.