Browse Google without being logged in while still logged into Gmail
To use Google, aka Google Search, without being logged in while you are logged in Gmail, use one of the following:
1: Two different web browsers
2: Use two different web browser profiles
3: Use two windows of the same web browser, one in regular navigation mode and the other in private navigation mode 1
The above is because Google Inc. now use a only one login for most of their web services, so once you sign in almost any Google web service you will be logged in most the the others.
1 : In Google Chrome the private navigation mode is called incognito mode.