The simplest answer is it classifies things by drawing a line between two groups of data points. From the linked wiki "More formally, a support vector machine constructs a hyperplane or set of hyperplanes in a high- or infinite-dimensional space, which can be used for classification, regression, or other tasks." The hyperplanes being the "lines" and a high dimensional space meaning you track a bunch of types of data about the things you want to classify. Say you want to know how likely it is to rain tomorrow based on what you know today. You could record the temperature, wind speed, humidity, time of the year, number of days since it last rained, etc.