To use GeForce Now, your device should support 64-bit Windows OS. It also needs an internet connection with at least 15Mbps for 720p at 60 FPS and 25Mbps for 1080p at 60 FPS. Other than that, here are the hardware requirements:
Dual core x86-64 CPU with 2.0GHz or faster
4GB of system memory
GPU that at least supports DirectX 11
NVIDIA GeForce 600 series or newer
AMD Radeon HD 3000 series or newer
Intel HD Graphics 2000 series or newer