You must have the MetaMask extension installed in your browser.
Go to https://app.1inch.io/;
click on ‘connect wallet’ and select the first option - ‘MetaMask’;
confirm connection to https://app.1inch.io/ in MetaMask.
Now you can operate with 1inch in your desktop browser and confirm transactions through the MetaMask extension.
iOS and Android
The best way to connect the MetaMask app to 1inch on your mobile phone is by using the MetaMask app’s internal browser.
Open the MetaMask app on your mobile phone;
click on the ‘menu’ button in the upper left corner;
click on the header and type app.1inch.io in the URL field;
on https://app.1inch.io/ choose ‘connect wallet’, accept the Terms of Service and select the first connection option - ‘MetaMask’.
You can now use the MetaMask internal browser for interaction with 1inch.
To connect the Metamask app on your mobile phone to a browser on your desktop, use the 'WalletConnect' option.
In a desktop browser, go to https://app.1inch.io/;
click on ‘connect wallet’, accept the Terms of Service and select 'WalletConnect'. A QR code will be displayed on the screen;
on your mobile phone, open the MetaMask app;
click on the "menu" button in the upper left corner;
in the upper right corner, click on the ‘QR-code scanner’ icon and point the phone’s camera to the QR code on the screen;
confirm connection on your phone.
Interact with 1inch in your desktop browser and confirm transactions from your phone.