about.md - how to use decorators

Author: mathstrains21

concepts/decorators/about.md

@@ -1,2 +1,51 @@
-#TODO: Add about for this concept.
+# About
+
+Decorators are a feature of the Python language that can modify or register a function.
+
+## How to use them
+
+Decorators are placed just above a function in the code like so:
+
+```py
+@decorator
+def function():
+    pass
+```
+
+Some decorator functions take arguments:
+
+```py
+@decorator2(name="Bob")
+def function2():
+    pass
+```
+
+If a decorator function takes any arguments, but you don't wish to pass any, you must still call it with parentheses for the decorator to work:
+
+```py
+@decorator3()
+def function3():
+    pass
+```
+
+Decorators are just syntactic sugar.
+An alternative way of doing the same as the above three examples is using higher-order functions:
+```py
+def function():
+    pass
+
+function = decorator(function)
+
+
+def function2():
+    pass
+
+function2 = decorator2(name="Bob")(function2)
+
+
+def function3():
+    pass
+
+function3 = decorator3()(function3)
+```