Question: In MicroSoft Dynamcis AX 2012, I'm very confused about those **Links** and **reference Data Sources** under Form's DataSource node. 

What do they do there? How they get there?

![enter image description here](https://i.stack.imgur.com/Zleog.jpg)

Answer: 
Have a look at what MSDN says about them : <http://msdn.microsoft.com/en-us/library/gg845085.aspx>

Basically reference datasources are used when you have a foreign key field in your datasource. Instead of showing the foreign key value of your table on your form, you can use fields from the reference datasource to show you more meaningful fields instead of the surrogate key value.

I use them often to be the better alternative than simple display methods. SQL joins the record and has all of the needed fields available instead of having to execute all of those display methods.
What's also nice about them too is you don't have to add umpteen data sources for reference usage, and not having to worry about accidentally deleting/inserting/updating values in that table (when you forget to change the AllowEdit/AllowDelete/AllowCreate and/or overwrite the write() method)