Best practice to use relations in forms

There is one model with relations one to many to another model.

What is the best way to create a form with fields from one model and add there fields from another model.

Unfortunately I did not found any information about this.

Is there some examples?

Like this? http://www.yiiframework.com/doc-2.0/guide-input-multiple-models.html

Yes, it is really what I need, I don’t now know why didn’t I found it myself