How change in TWO child component can result in change in Parent component's Output?

Here I have college task to do..where i got stuck in the middle.! I have two child component one is having the checkboxes to filter the result while one has the detail of the output to be display.Now I am done with the outer part i.e. layout but now getting confused how to imply its functions and all, guys please help me with this as i am doing this since last 1 and half days.

https://stackblitz.com/edit/angulaar-aman?file=src%2Fapp%2Fapp.component.html

here is the work i have done till now..!!