You can use both the Metamask browser plugin or the Metamask mobile app if you want. Here, we will show the instructions for the browser plugin: for the mobile app, the configuration is very similar.
1. Add a custom RPC/Network
In the Metamask browser extension, open the "Networks" drop-down menu at the top, and choose the "Custom RPC" menu item:
2. Mainnet and Testnet network configuration
Input the respective network values for IoTeX Mainnet or IoTeX Testnet (see how to Access the Babel API doc for the actual Network parameters):
3. Save and select the IoTeX network
Click the Save button and make sure IoTeX is selected as the active network: