There are plenty of Google secrets out there, a lot involve changing the interface of the Google Search engine. Such as having it slightly tilted, a Star Trek theme, or using it in a purely text environment. But I wanted to present some tricks that aren't so much secrets as they are normal features that can be used in meaningful ways people often don't think of.
1. Google Images
Now, what this is good for is a couple of things. Sometimes you need to find articles on a particular subject that has certain images, but you don't know the correct search criteria to use. Chances are you can find it in Google's search results, but if not, you can use Google Images. If the article is mentioning specific, let's say a celebrity at a red carpet affair, you can type in something like "Kim Kardashian red carpet" into Google then select the Image tab. Hopefully it will return images of Kim on the red carpet. You can then click the image to not only enlarge, but to visit the webpage that is hosting the image which may be an article will all the gossip on her attire, or whatever.
Sometimes images are banned by certain ISP's (or countries). Instead of being met by blocked websites, you can type in what the pictures are about into Google and use its Image tab again. While the actual websites that host the images may be banned, the images should show up for viewing.
If you want to access the actual website check out my third "secret".
2. Google Image Search
Google has its own image search that is more along the lines of a reverse image search. You upload or take a picture and fill out what information you can on the image in Google Image Search. It will then try to find more images related to that image (with webpage links to sites hosting the related images). It is meant to be helpful when trying to find the name of something, where to buy it, who created it, etc.
My own experience has not been great with Google Image Search. A couple of weeks ago my wife received a belated birthday gift, which was a bag by Michael Kors. There were no tags so we could not easily discern what model and type it was. I uploaded a smartphone photo to Google Image Search and typed in "Michael Kors bag", along with the color. It came up with a lot of Michael Kors items, including bags and shoes, but nothing that was identical to the photograph...
3. Google Cache
I use this trick quite often. When you search on a desktop, you will usually see little green arrows next to the URL of each search result (under the title of a link). For mobile users, you will need to click on the settings of your mobile browser and request to view as a desktop site before you can see these little arrows. This will give you the option to view a cached version of websites.
This may seem unimportant, but it can be very useful. If your ISP (or country) bans certain websites, this is a way to get around their restrictions. You no longer have to use a proxy or VPN in order to access certain webpages. The only problem is trying to go to other links that are from within those websites. You will need to copy the link and post it in Google and repeat the process to view other pages in those websites.
Another way this method can be useful is for research purposes. Maybe you are looking for a certain webpage that no longer exists. If you're lucky, Google has a cached page of it. You would just insert the link into Google and see if it has it.
4. Index of
This would be considered a Google secret, and one I have used for years. Servers have the default name of "index of". Because of this, you can use this trick to search servers with that name for different files.
"index of:" Example of File Name
That's pretty much it. Google will then search for your criteria and give you any results that gave hits.
If you want to get more specific, you can list file types to narrow down your search. For example, if you wanted to find a certain song, you could type:
"index of:" (mp3|wav|aac|flac|ogg|opus) Song Title
Notice that the file types are all separated by dividers. You can put as many or few file types as you want, and can even mix in video or other types into it.
5. Google Voice Number
If you have a Google account (Gmail, Google Drive, etc.), and you live in the US or Canada, you have the ability to add a phone number in Google Voice. The process is simple and will require a mobile number for verification. While this is not a secret, what you can do with it is.
If you travel a lot, or happen to move to a foreign country, you can setup your iOS or Android device to make free phone calls back to the US or Canada (as long as you have WiFi). On an iOS device you will need to download a free app called Talkatone. On an Android device you can download Talkatone or pay for Spare Phone (which is by far superior in audio quality). You then add your Google account information and it will allow you to make as many free calls as you want.
Alternatively, you can use your computer and login to your Google Voice account to make calls and texts. Gmail will work for just calls, but I have noticed that if you are using a certain theme you cannot get the phone icon to display.
This is more of a secret for Android users. The Play Store is great for updating apps, but Aptoide can be better. Aptoide does host illegal apps, but you should only use this market store as a way to get the latest updates.
Aptoide can't be downloaded on the Play Store, so you will first need to ensure that the option to download outside sources is enabled in Settings > Security. You can then use any web browser to type in "Aptoide download" in Google, and click the first link which should be Aptoide's install page. Click the install button on the webpage, the app will download, and once done a prompt to install it will appear.
Open Aptoide and click the "Updates" tab. It should load up the newest versions of your apps, even Google apps like Play Store!
Note: This is not meant as a replacement for the Play Store, however, it can be if you have an Android device that does come with it...