Step 1: Open the official download site
Visit letsvpnshield.com in your browser, choose the version that matches your device, and avoid install packages from unknown sources.
Step 2: Install and grant permissions
Complete the install per the system prompts; Android needs Unknown Sources allowed, and on iOS just trust the profile per the guide.

Step 3: Open the app and one-tap connect
On first open you can connect and try it without registering; tap Connect to reach a node worldwide in 3 seconds.
Step 4: Register to sync across devices
To recover membership on a new phone or share across devices, register and bind with email and password under My.
Sources: LetsVPN Official, Official Download, Apple Support, Microsoft Support and other public references.