Macros can be used to perform simple repeated tasks. The idea is similar to macros in other Office applications.
Macros are built using a sort of scripting language called Macro Language. An extensive documentation and tutorial on Macro Language is available here: Documentation.
Macroland is a place where you can download macros. Check them out here and start downloading macros. Using Macro Editor, you can inspect those macros, play with them and modify them, and start building your own macros. You can also easily share the macros you build with other users. See this post for more information.
Here are some of the macros you can download from Macroland: