Note: You cannot develop react-native apps for iOS on Windows, only react-native android apps.
The official setup docs for react-native on windows can be found here. If you need more details there is a granular guide here.
Tools/Environment
1) Setup your machine for react native development
Start the command line as an administrator run the following commands:
choco install nodejs.install
choco install python2
Restart command line as an administrator so you can run npm
npm install -g react-native-cli
After running the last command copy the directory that react-native was installed in. You will need this for Step 4. I tried this on two computers in one case it was: C:\\Program Files (x86)\\Nodist\\v-x64\\6.2.2. In the other it was: C:\\Users\\admin\\AppData\\Roaming\\npm
2) Set your Environment Variables
A Step by Step guide with images can be found here for this section.
Open the Environment Variables window by navigating to:
[Right click] “Start” menu -> System -> Advanced System Settings -> Environment Variables
In the bottom section find the “Path” System Variable and add the location that react-native was installed to in step 1.