That's okay! Companies might be making money by serving you relevant ads, but in turn they provide you a valuable service, most of the time for free.
In reality, the sophisticated technologies we use everyday would not be possible without knowing some information about their users.
Services often keep a history of items you've viewed. Here are some examples of popular services that makes the information they collect about you public.
Facebook's ad preferences page (https://www.facebook.com/ads/preferences) shows you a list of interests associated with your account on what they think you are interested in.
Facebook allows you to download a copy of the data Facebook has on you on their Download Your Information page (https://www.facebook.com/dyi), including every post you've shared, all the groups you're associated with, all the events you've visited, all of your search history on Facebook, the informationn advertisers collected from you, and many more.
Google Maps's timeline page (https://www.google.com/maps/timeline) by default stores all of the location you've visited (using Android location services or Google Maps).
Apple iPhone users by default have their location tracked, anonymized, and sent to Apple. (https://www.businessinsider.com/how-to-see-your-iphone-location-history-2015-11) includes a tutorial on how to view this on your phone.
Twitter also allows you to download a copy of the data they have on you on their Your Twitter Data page (https://twitter.com/settings/your_twitter_data). It includes locations, interests, ad-related data, etc.
Note that these examples are just data the companies have selectively released in a consumable format. There are a lot more information and data they collect to allow them to build services that give them advantages over competitors.
To protect yourself, you should review the privacy policies of the products you are using and be aware of what companies are doing with your data. If you are signing into a new app or website that allows you to use Facebook or Google sign-ins, you should review the items that you're actually sharing.
Some platforms allow you to change your privacy settings to limit the amount of information you're sharing.
Of course, this is just an incomprehensive list of popular products. You should practice caution before using new services and limit the amount of information you share until you 100% trust the company you use.