This Seeking Tech guide will show you how to buy PSN avatars on the PlayStation 4. To do so, you need to do the following:
1. From the home screen, go to Profile.
2. You then need to select the three dots option.
3. Afterwards, select Edit Profile.
4. From the Profile screen, select Avatar.
5. Next, you need to select Premium Avatars.
6. You then need to scroll down the list and then select the Get More Avatars option.
7. You should now see a list of avatars that you can purchase.