Client–Server
Every interaction on the web is a request from a client and a response from a server. Master this and the rest of the web makes sense.
HTTP & HTTPS
The protocol clients and servers use to talk. What HTTP looks like, why HTTPS is mandatory, and which version you're actually using.
TLS & HTTPS internals
What the "S" in HTTPS actually does — the TLS handshake step by step, the certificate chain (root → intermediate → leaf), Certificate Authorities, SNI, Let's Encrypt/ACME auto-renewal, and a brief look at mTLS for service-to-service.
Methods & Status
The verbs (GET, POST, PUT, PATCH, DELETE) and the numeric replies (200, 404, 500) that make up every HTTP conversation.
Headers & Cookies
How HTTP requests and responses carry metadata, and the cookie mechanism that lets stateless HTTP remember who you are.
DNS
How a name like google.com becomes the IP address 142.250.190.78, and why this happens in milliseconds despite being a multi-step lookup.
CDN & Edge
Why your website is fast for a user in Tokyo even though your server is in Virginia. CDNs cache copies near users; the edge runs code near users.