Business Data related list will be filtered as per the connected Business Data list webpart.
Ok then Let start.
1) Open your page in edit mode -> chose insert webpart and select Business Data List Web part. Now edit webpart and choose your External entity.
Here I have Chosen Project Entity.
2) Next add Business Data Related List Webpart and edit its property. Choose related entity. Here I have chosen Employee entity. Here you need to configure the Association method. This entity should have association method.
The Relation between Employee and Project Entity is like Each Employee is assigned to a Project. Now We need to display all employees that are assigned to a particular project.
3) Make sure you have Allow Connection checked and the Business Data Relation List Web Part connected with Business Data List web part.
That’s it. We have configured our Business Data Related List webpart.