Query Builder need help

It is not a Query Builder example. It is an example of CodeIgniter\Model.

But it is very confusing because CodeIgniter\Model could use Query Builder's methods.

OK thanks for understand of query builder, maybe you know how i can send $var to query builder?

I want to do that in Contacts page i see all contacts its ok and working but i need make on click button to show only one contact card i think i make onclick send $var to query buuilder where('id', $id) and get only one contact card, but i cant understand how to do and correct do, because in controler i can make this working but i know its not correct

i need help how send $var from Controller to Model