You can download an Electrum wallet through play store depending the phone you are using, if you are using iPhone you can use an app store but if you are using android phone you can go with a play store to download Electrum wallet and perform your registration and write out your seed phrase immediately and document it safely
The right place to download Electrum wallet is from the official website, and even after downloading you should verify your download before using it. Take note too that Electrum is not available on IOS, if you want a good BTC wallet for IOS you should use BlueWallet, it is a recommended BTC wallet. There's also nothing like registration on Electrum wallet, registration is for centralized services, after downloading and verifying your Electrum wallet, you simply choose the type of wallet you want and generate the seed phrase and keys.