The "hosts" file is located in the following path:
C:\Windows\System32\Drivers\etc\hosts
You can open it with any text editor or Notepad. Under almost all circumstances, it should contain only one line that does not begin with a "#" character and that line should be:
127.0.0.1 localhost
Malware often uses the "hosts" file to redirect to different sites -- so if you think you are going to your bank's website, you might instead be going to some other site and typing in your account login and passwords.
In general, do not allow changes to your hosts file. The very fact that something tried to change it is indicative that you have some kind of malware on your machine. Download a program such as "Malwarebytes " and do a thorough scan of your machine.
HTH,
JW