 So, you may be wondering, how do you find anything at all on the web? What if you don't even have an idea of what's available, let alone how to get there? Well, that's where you use a web search engine. Web search is a service offered by a number of companies, primarily Google, Yahoo, and a service from Microsoft called Bing. The way this works, for example, is that I go to Google's web page, and for that I just have to remember that their address is http colon slash slash google.com. And on their web page, they have a text box where I type search terms, things I want to search for, and then I click the button that says search. And that takes me to a page that shows search results for what I entered. So if I enter the text ducks and click the button, I'll get back this page with a list of links to web pages about ducks. How this works is that Google has machines that do nothing but spider the web, meaning it goes out to random pages, it follows all the links on all the pages it can find, and as it does so and retrieves these pages, it makes a textual index of all the text on all those pages. Now, it turns out the real tricky part is deciding in which order to display any relevant results. Like in this case, when I search for ducks, it turns out that Google has 14.5 million different pages that match the term ducks. And Google has to decide which of those 14.5 million pages I most want to see, which ones should go at the top of the results. In general, Google and the other search engines try and order their results by popularity. So generally, when you see a link at the top of the results page, it's because it's a popular link. Now, you may be wondering, how do they make money from providing the service? Well, the answer is that they sell advertisements. When you look at the Google's results page, that column off on the right, you'll see in faint gray text at the top, it's labeled sponsored links. That whole column off on the right, those are advertisements. Advertisements which do have something to do with what you searched for, but these particular links you're seeing because someone paid money, not because they're necessarily popular. So far, Google and the other search providers try hard not to mingle advertisements with the proper search results, because they know that users want to see search results that aren't contaminated with pay for play. When I search for ducks, I probably want to see at the top of the results an informative page about ducks, not a page that's trying to sell me something. For most users of the web, there are sites which they go to over and over again. And so browsers have this mechanism called bookmarks for keeping track of websites you have visited before. When you're looking at a web page that you know you'll want to come back to later, you can click on this little star icon to bookmark that page. The bookmark is simply a record of the title of that page and its URL. And so you can get back to a page by clicking on a bookmark in your web browser's list of bookmarks. However, you must understand this won't necessarily take you back to the page exactly as you saw it. As I explained before, many web pages these days are dynamically generated by the web server. And so when you have your browser go to the page at a certain URL, the web server might change what page it sends back every time that URL is visited. Something might be changing on that page. Now, if there's some page that you really want to make sure you can preserve so you can get at it again exactly as it was, it is possible to save a page to a file so that you can open it later from your local system. And that ensures that you can get back to a page even if it's taken down from the location where you found it. So the web is the part of the internet, which people spend most of their time with, but it's not the whole internet. There are other things we can do with it, including email. Email is a separate application from the web. In fact, it doesn't use HTTP. It uses these other protocols, SMTP, POP, and IMAP. To send and receive email, you need an email address. And these addresses have the form of a username followed by the at symbol, which looks like an A with a circle around it, and then a domain name. The domain name is the part of the address which specifies where an email message should be sent to on the internet, and the username specifies the recipient at that location. The way the system works is you need both email servers and email clients. The servers are responsible for actually sending the messages and storing any received messages, and the clients are the programs which users actually interact with on their own systems. So for example, here in this diagram, when Nathan at apples.com wishes to send an email to Kate at orange.net, Nathan composes the message in his email client, and then his email client sends it to his email server, and that email server sends it to Kate's email server, and the email sits on that server until Kate checks her email with her email client. Typically, when you sign up for internet service, your service provider gives you an email account on their email server, and then you can interact with that account using an email client on your own system. Two popular email clients include one from Microsoft called Outlook, and a free one called Thunderbird, which is made by Mozilla, the same people who make the Firefox web browser. Rather than using an email client, however, many people these days simply use what is called webmail, which is pretty much what it sounds like. It's doing email using your web browser. For example, Google offers a webmail service called Gmail. If you go to the Gmail web page, you can sign up for an account and pick an email address. Then when you go to the Gmail web page and sign in with your account, it'll take you to a page where you can read your incoming mail and send new emails. So Gmail is probably the most popular webmail service right now. Another popular one is Yahoo Mail. So the web and email are the most popular things for users to do with the internet, but there are, of course, other applications, like, for example, games, and also instant messaging is very popular, and also this thing called VoIP-V-O-I-P, which stands for Voice Over Internet Protocol, meaning basically you can make phone calls over the internet using a microphone with your computer. And the popular program for that purpose is one called Skype.