Relation is a very important flexicontent field
it can create a "dynamic relation" between 2 contents. Like a book with his author, all fields between 2 items can be displayed dynamicly in each view wihout editing two item.
To acheive this wee need to create a relation field and a revers field !
For this site we create 6 relations / revers fields :
Now how it works
in editing tab configure your field to filter item wanted (categorie, order etc)
in viewing tab you can create your display loop with small html
any field can display with {{nameoffield##0}} (##0 is to select firt value in field)
For the revert create a reverse field
in editing tab choose your relation field for linking
in viewing tab you can filter your content return
And you can create your html output