I solved problem by following below steps
1) open Node.js command prompt
2) Then type "npm install create-react-app -g" (g for global access) command to install create-react-app
3) Then type "npm install create-react-native-app -g" (g for global access) command to install create-react-native-app
Follow step #2 for use create-react-app
Follow step #3 only if you want to use create-react-native-app otherwise its optional.