Constant nodes are a way to create a static value for use inside Functions. Unlike Variables, they can not be modified externally. Additionally, this page provides some extra information for each data type and its common usecases.
Constant Integers generate whole numbers, not fractional numbers. That means they can never have any values after the decimal sign, and always have to in- or decrease by steps of at least 1. Integers can be converted to Float, which will simply add a ".0" to their value, no data is lost or added.
An Integer, has a single component, the (1) is omitted from the name for brevity. Integer is quite common and used for any value that requires single choices: to set an amount, and even internally inside Drop Down Menus for something like a Multi Switch.
An Integer2 node generates a static 2-component Integer Vector. Components are named X, Y. Integer2 is not common, but is used for example to set X and Y 2D tiling in a Tile Generator.
An Integer3 node generates a static 3-component Integer Vector. Components are named X,Y,Z. Integer 3 is not common and is unlikely to be encountered much.
An Integer4 node generates a static 4-component Integer Vector. Components are named X,Y,Z,W. Integer 4 is not common and is unlikely to be encountered much.
Constant Floats generate fractional numbers, not wholenumbers. That means they will always have values after the decimal sign, and can in- or decrease by steps smaller than 1 (default 0.01). Floats can be converted to Integers. but they will be rounded up or down to the nearest Integer, meaning data and accuracy is lost.
A Float, has a single component, the (1) is omitted from the name for brevity. Float is very common and used for any value that requires precise control in the form of a slider or Angle. You can find it in almost every Node's parameters. It is also the preferred data type for a grayscale value!
A Float3 node generates a static 3-component Float Vector. Components are named X,Y,Z. Float3 is uncommon, it is mainly used to represent 3D scale coordinates, and as a simpler way to store color without Alpha data.
A Float4 generates a static 4-component Float Vector.Components are named X,Y,Z,W. Float4 is very common, as it is the preferred way to store and set Color information, where XYZW data represents RGBA values.
Two additional data types exist inside Functions: Booleans and Strings. Strings were only introduced alongside the Text node in Substance Designer 6.
A Boolean is the simplest data type there is, knowing only two states: True or False, 1 or 0. It is represented by the color white. It is not possible to interchange between Boolean and Integer without Casting, or by using Logical Nodes. A Boolean is quite common and it's an excellent way to control the flow of a function or graph, a typical use would be for a Switch Node.
A String Node generates a static String, a piece of text. It is the most exotic type of Data available in Functions, and generally can not be used much in conjunction with other Function nodes. It's main goal is to function as a final output for the Text Node.