The answer is “A lot!”
Go to MyAccount.Google.com
Google will walk you through the settings and help you choose your preferences.
Or look at the individual sections to change your preferences.
Change each setting for your preferences.
Google follows what you search for and develops a “profile” for you. They narrow down your search results then to fit your profile. If you do a search that gets strange results, you can delete it from History to keep your profile more clear.
You can turn off tracking or delete your history.
It is worth your time to check the Google settings. You want to give enough info to have good search results but not enough to display your whole life to the Internet.