How to check users device?

Hello everyone! I want to create website for my friend.

When user visit website from PC, he will see the menu, photos and other things. But if he visit website from Android smartphone, he must see the link to Play Market store (where will be app of this website).

If user visit website from iPhone/iPad, he will see the link to App Store. 

I see that idea here https://iq-option.bid/ but i dont know ho do it. 

Can you help me with it?