What can I encode in a QR code?

URLs, plain text, email addresses (mailto:), phone numbers (tel:), SMS (smsto:), WiFi credentials (WIFI:S:name;T:WPA;P:pass;;), and geographic coordinates (geo:lat,lng).

What does error correction level mean?

Error correction allows the QR code to be scanned even if partially damaged. Level L (7%) is for clean environments; Level H (30%) is recommended if you plan to overlay a logo.