To use AMD Freesync, there're some requirement with graphics cards, graphics drivers and certified monitors.
1. A compatible AMD Radeon™ GPU with a DisplayPort connection.
AMD Radeon™ R9 Fury X, Fury, Nano, R9 390X, R9 390, 295X2, 290X, 290, R9 380, 285, R7 360, 260X and 260 GPUs feature display controllers that support dynamic refresh rates during gaming.
2. A compatible AMD graphics driver.
AMD FreeSync™ is available using the latest AMD graphics drivers from www.amd.com/drivers.
3. A certified or compatible monitor with AMD FreeSync.
As of Oct 13, 2017, the following Viewsonic monitors are compatible with AMD FreeSync™ technology.
Viewsonic XG2401, XG2402, XG2530, XG2700-4K, XG2702, XG2703-GS, XG2730, XG2740, XG3202, XG3240, VP2468, VP2768, VP2785-4K, VP3268-4K, VP3881, VX2257-MHD, VX2457-MHD, VX2757-MHD, VX2716-SCMH, VX4380-4K
Please enable FreeSync in monitor's OSD menu and AMD Radeon software.
1. An example of XG2401 OSD menu where to turn on FreeSync.
2. How to enable AMD Radeon software?
Please refer to the details procedures in the FAQ from AMD support site.