Usage Of LinkMap

I may have overlooked this, but it’s unclear to me from the documentation how a LinkMap and EmbeddedMap are used exactly. The documentation states that a LinkMap is:

Ordered map of links, with a String key, which also doesn’t accept duplicates.

It’s unclear to me what the “String” key actually is and how the LinkMap is used in practice.

Could someone point me to an example in the documenation or provide an example?