Most browsers these days have an incognito mode. When you open this private mode, you can surf the internet without your surfing behavior and internet data being tracked by the browser. The cache is empty. Every time you close the incognito/private window, all your data is deleted, such as your login information and cookies.
You can use an incognito/private window if you don't want to log out of your normal window but login with another account (e.g. a test account), or to see what a page looks like when the cache is empty and no cookies are set. Cookies and cache can influence webpage behaviour, which you can read in the article "Why can't I open a page/login/why do I get an URL error?". You can read more about the cache in this article.
The following table shows how to enable incognito mode in different browsers.
METHOD USING THE MOUSE
METHOD USING SHORTCUTS
Settings (top right) > New Incognito Window
Ctrl + Shift + N
Settings (top right) > New InPrivate
Crtl + Shift + P
Settings (top right) > New Private window
Ctrl + Shift + P
Settings (top right) > Private mode
Shift + Command + N