To Make Fully Defined Assembly You have to make all parts fully dimensioned of fully constrained as in this tutorial. I will give a example of your components. as under..
First of all Insert a component as you can this is fully defined because this is automatically fixed.. This can not be moved..
Insert another component anywhere .
Select outer surface of small pin And select internal surface of first part as in picture.
Select concentric mate so that pin can slide in the hole..
Similarly select two front faces of both parts.
Select coincident mate so that pin can only rotate in the hole.
Similarly select right (or top) planes of both parts.
Select coincident mate so that pin even can not rotate.
Finely we can see this assembly is fully defined.