How can I establish an AD-HOC Wi-Fi connection on my tablet? I'm not an expert in this kind of subject. I'm reading that I need to root my tablet.

What does root mean? All the instructions are really difficult.

How can I make this AD-HOC Wi-Fi connection in my Sony S tablet? 

I'm running Android 4.0
There are two other Q&amp;As here which might help you (in fact, there are several more, but most of them -- as you wrote -- are a bit "techy" or, as you put it, "really difficult"):


Does any version of Android support ad-hoc connections? could be used ith the second device involved is running Windows, and seems not to involve rooting your device
Connect android phones through adhoc wifi network is just "slightly techy", but requires root, and the Android SDK on a computer


If rooting your device is no problem for you, the second approach should be possible also without the SDK -- if you have a terminal emulator such as Android Terminal Emulator installed on your Android device. You could then execute the commands quoted there within the terminal emulator, but probably need to prefix them with the su command (to have them run by root):

su ifconfig wlan0 up
su iwconfig mode auto;iwconfig wlan0 essid "your SSID" channel 11 mode auto
su ifconfig wlan0 10.0.0.x netmask 255.255.255.0


As explained,


  your SSID should be replaced with the name of your Adhoc network, and 10.0.0.x is a different IP you give each device.


I didn't test/verify that, but from my Linux knowledge, it sounds quite reasonable. Drawback is, you would need to execute those commands each time you need to establish the ad-hoc connection -- but here some other app could kick in, once you verified the steps are working. One I found is Script Manager - SManager -- but there were some easier ones I just cannot remember at the moment. If this is an acceptable approach to you, I can update my answer and add a few more tools to compensate.

EDIT:

Here's the one I had in mind to make the script-running easier: Scripter