Dynamo generally operates using 3 x types of data – Numbers, Strings & Booleans.

1. Numbers = Integers (Whole Numbers) or if Dynamo requests a Double it wants a decimal “1.2” is 2 number’s, hence Double. (Double is a Computer Science term).
2. Strings = these are sequences of text, they can also be used to update Revit parameters for example.
3. Booleans = This is simply either “True” or “False”. For example is 5 less than < 10, this would return a “True” output.

If you hover over an Input port, as shown below, it will state what Data type it can take in. The below example node accepts a Double or the Default value is 0.