You have 2 main options.
1. PS4 Extended Storage USB HDD
Format a USB HDD on the PS4 as Extended Storage and then install or move the games to that.
This is the easiest and most simple method.
On the PS4 go to Settings > Devices > USB Storage Devices >
Select Your USB Drive > Format As Extended Storage
2. AppToUSB
Format a USB HDD as exFAT and use stooged's AppToUSB.
This is a more complicated method but instructions can be found on the PS4 AIO Guide
here. (look for 'USING APPTOUSB')