When you type a web address (called a URL, for Uniform Resource Locator) and press Enter, your browser does four things in about a second: it reads the address, finds the server, asks for the page, and builds it on your screen. Follow each step below.

Reading a Web Address
Reading a Web AddressA browser address bar showing https://www.numu.tech/about with each part colored and labeled: scheme, subdomain, domain name, top-level domain, and path.READING A WEB ADDRESShttps://www.numu.tech/aboutSchemeSubdomainDomain nameTop-level domainPathRead it left to right: how to talk, which website, which page.12345
Read all 5 details
  1. 1Scheme. https:// is the scheme. It tells the browser how to talk to the website. HTTPS stands for Hypertext Transfer Protocol Secure, and the "S" means secure: the conversation is scrambled so others on the network cannot read it.
  2. 2Subdomain. www is a subdomain, a section of a website's name. Many sites work with or without it.
  3. 3Domain name. numu is the name the website's owner registered. Domain names are easy for people to remember, unlike the number addresses computers use.
  4. 4Top-level domain. .tech is the top-level domain, the last part of the name. Others include .com, .org, .gov, and .edu.
  5. 5Path. /about points to a specific page on the website, like a room inside a building.
Finding the Server: DNS
Finding the Server: DNSA laptop asks a DNS resolver for numu.tech. The resolver asks a root server, then a .tech server, then the numu.tech server, and returns the IP address 203.0.113.25 to the laptop.FINDING THE SERVER: DNSnumu.tech?DNS resolverRoot server.tech servernumu.tech server203.0.113.25123456
Read all 6 details
  1. 1You type a name. Computers find each other by number, but people remember names. When you type numu.tech, your device first has to find that site's number, its IP (Internet Protocol) address. The system that does this is called DNS, the Domain Name System.
  2. 2Ask the resolver. Your device asks a DNS resolver, usually run by your internet service provider (ISP). Think of it as a librarian who knows where to look things up.
  3. 3The root. If the librarian does not already know, it asks a root server. The root does not know the answer, but it knows who handles every name ending in .tech.
  4. 4The .tech server. The .tech server points to the name server that holds the official records for numu.tech.
  5. 5The final answer. The numu.tech name server answers with the IP address, such as 203.0.113.25.
  6. 6Back to you, and remembered. The resolver hands the address to your browser, which can now contact the website. The answer is saved for a while, so the next visit skips most of these steps.
Asking and Answering: HTTP
Asking and Answering: HTTPA browser sends a GET /about request through a locked HTTPS tunnel to a web server, which answers with HTML, CSS, JavaScript, and image files and the status 200 OK. Badges show 200, 301, 404, and 500 codes.ASKING AND ANSWERINGYour browserWeb serverGET /aboutHTMLCSSJSIMG200 OKHTTPS200 OK301 Moved404 Not found500 Server error1234
Read all 4 details
  1. 1The request. Your browser sends the web server a short message, like "GET /about," which means "please send me the About page." This shared language is called HTTP (Hypertext Transfer Protocol), and GET is its word for "send me."
  2. 2The answer. The server sends back the files that make up the page: HTML, CSS, JavaScript (JS), and images (IMG). A big page can be dozens of files.
  3. 3Status codes. Every answer starts with a three-digit code. 200 means OK. 301 means the page moved. 404 means not found. Codes in the 500s mean something went wrong on the server's side.
  4. 4The padlock. HTTPS (the secure version of HTTP) seals the conversation like a locked envelope, so others on the network cannot read or change it. The padlock means the connection is private. It does not prove the website itself is honest, so still be careful where you type passwords.
Three Building Blocks of Every Page
Three Building Blocks of Every PageThree houses: a bare wooden frame labeled HTML structure, a painted house labeled CSS style, and a house with glowing lights and a ringing doorbell labeled JavaScript action.THREE BUILDING BLOCKS OF EVERY PAGE<h1><p> <img>HTMLSTRUCTURECSSSTYLEJavaScriptACTIONYour browser puts all three together1234
Read all 4 details
  1. 1HTML: the frame. HTML (HyperText Markup Language) is the structure of the page: the headings, paragraphs, pictures, and links. It is like the frame and walls of a house. Tags such as <h1> for a heading and <p> for a paragraph mark each part.
  2. 2CSS: the paint. CSS (Cascading Style Sheets) controls how the page looks: colors, fonts, spacing, and layout. It is like the paint, furniture, and decorations. The same HTML can look very different with different CSS.
  3. 3JavaScript: the wiring. JavaScript, often shortened to JS, is a programming language that makes the page respond when you do something, like opening a menu, playing a video, or checking a form before you send it. It is like the electrical wiring that runs the lights and the doorbell.
  4. 4Your browser builds it. Your browser reads all three and paints the finished page on your screen in a moment. On most computers you can right-click a page and choose "View page source" to see its HTML.

Remember

numu.tech

A web address says how, which site, and which page

DNS turns names into numbers

</>

HTML builds it, CSS styles it, JavaScript makes it move

Try it

1. What does DNS (the Domain Name System) do?

2. A page says 404. What happened?

3. What does the padlock next to the address mean?

Learn more

References

  1. Cloudflare. (n.d.-a). What is DNS? Cloudflare Learning Center. https://www.cloudflare.com/learning/dns/what-is-dns/
  2. Cloudflare. (n.d.-b). What is HTTPS? Cloudflare Learning Center. https://www.cloudflare.com/learning/ssl/what-is-https/
  3. Code.org. (n.d.). How the Internet works [Video series]. https://code.org/videos
  4. MDN contributors. (n.d.-a). How the web works. MDN Web Docs. https://developer.mozilla.org/en-US/docs/Learn_web_development/Getting_started/Web_standards/How_the_web_works
  5. MDN contributors. (n.d.-b). HTTP response status codes. MDN Web Docs. https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Status
  6. MDN contributors. (n.d.-c). What is a URL? MDN Web Docs. https://developer.mozilla.org/en-US/docs/Learn_web_development/Howto/Web_mechanics/What_is_a_URL

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