Understanding TCP and UDP is essential for developers building networked applications. TCP ensures reliable, ordered data delivery through connection handshakes and error correction. UDP prioritizes speed with minimal overhead, sending packets without guarantees.

HTTP operates at the application layer and depends on TCP for reliable message transmission. When you load a webpage, HTTP defines the request/response format while TCP handles packet delivery. Most web traffic still relies on this TCP foundation.

Choose TCP for applications requiring complete data integrity like file transfers, email, and API calls. Opt for UDP in real-time scenarios like gaming, video streaming, and VoIP where low latency trumps perfect delivery. Newer protocols like HTTP/3 experiment with UDP-based QUIC for performance gains.