The ways in which you're tracked are extensive and some even sound like science fiction, however they're all proven to be real and true by the services that use them, people within the tech and privacy community, and even by government whistleblowers.
Starting with your phone, this is one of the biggest and most vulnerable entries into your private life. You bring it everywhere and keep all kinds of information about yourself on it, so obviously it's going to be targeted the hardest. There is tracking through your browser, but the biggest way they wriggle into your privacy is through apps.
- You'll download a social media app or mobile game, and it'll often have options to link with other services. This usually provides little to no benefit, but effortlessly gives these companies a wider range of information they can put together to learn more about you. An example would be Candy Crush linking with Facebook. You may be given some sort of reward in the game but this is just to give you an incentive to make you do it. It allows Facebook and Candy Crush to combine the information they've learned about you such as who you, what things you like, and what ads you respond best to, increasing their power to advertise to you and track you better.
- Apps often ask for device permissions to "unlock features" and somehow enhance your use on the app, however this is almost always a guaranteed way to track you and others. For example Snapchat's Snap Maps allows you and all your friends to permanently turn on your location to always see where eachother are, but this just gives Snapchat (and also complete strangers!) information about where you live, who you hang out with, what stores you go to, etc.
- Though even if you disable location privileges in an app, you still may not be safe! Another location tracking technique is through the metadata of your photos. By default, many phones have location data tied to every photo you take, usually to let you see a map of where you've been and what you took pictures of. However, any apps that have access to your photos will also get access to this metadata, in turn allowing them to see your location as well, which seems like a scarily desperate method.
- Another tracking technique is by asking for your contacts, like for example when Facebook does so you can see which of your contacts use Facebook so you can add them, however this also allows Facebook to see which of your friends don't use Facebook. This gives them new people to target or adds more to what they know about someone.
Now going onto ways to track your computer and just browser use in general, this is where it becomes more technical.
- Every internet user has an identifiable piece of information called an IP address. It's given to every website or service you connect to and in short, it's your Internet address. With this however, anyone or any service can find out what your physical location is. Knowing this, you can probably already see the vulnerability. Any website you connect to will get your location unless you specifically safeguard against this. Plus with being able to see your location, websites are able to see if you're a repeat visitor, essentially letting them profile and track you even if you don't use an account.
- Another way of tracking is called fingerprinting. The device you use has characteristics that when looked at altogether can be unique enough to accurately identify you. For example a website can detect what browser you use, what your screen resolution is, what default language is on your device, and many other things. And while this information on its own would be useless, putting it all together usually shows an almost unique configuration for each user, giving them a way to differentiate and track users.
- When you go onto a website, there's a good chance it'll ask if it's okay to enable cookies, so most people are already familiar with them. They can save many things, but specifically they usually store what pages you've been to, what you've searched for online, when you click an advertisement, and what time you arrived on a site.