This article explains how to sync Facebook contacts on a Samsung Galaxy S8.
Steps

Step 1. Open Facebook on your device
The icon is represented by a white "f" on a blue background and is located in the app drawer. If you are not already logged in, please do so before continuing.

Step 2. Tap ≡ in the upper right corner of the screen

Step 3. Tap Friends in the menu on the left side of the screen

Step 4. Tap the Contacts tab at the top of the screen

Step 5. Tap Get Started
This blue button is located at the bottom of the screen.

Step 6. Tap Allow in the pop-up window
If this is your first time using Facebook, you will need to do so to start syncing your contacts. When synchronization is complete you will find your Facebook friends in the "Contacts" application. Remember that you will only find those who have provided their phone number and other contact information to Facebook.