On the Web, when you use the Pera Algo Wallet, you will be able to scan a QR code (similar to the below picture). If you scan this with your mobile, your wallet will be connected to xBacked.
Make sure if you are on testnet you enable the Pera Wallet to use testnet! You can do this by going to Settings > Developer Settings > Node Settings > Choose TestNet instead of MainNet
There are also several other wallets like Defly, Fireblocks and wallet connect options by clicking on the connect button at the top right corner of the screen