How run moisture sensors

Hi everybody, first of all sorry for my bad level in english, I'm French :grinning: (lel the ridiculous excuse), but I have a problem, for a school project, I must a lot of sensors, moisture of the floor http://e.banana-pi.fr/fr/capteurs/80-capteur-d-humidite-du-sol-funduino.html

and water sensor http://e.banana-pi.fr/fr/capteurs/91-capteur-de-niveau-d-eau-sa0081.html but I don't understand how it works, I know it's an analogic signal, but what is the link between the moisture and the frequency of the signal?

And what is about the DHT11: http://boutique.semageek.com/fr/138-dht11-capteur-de-temp%C3%A9rature-et-humidit%C3%A9-digital.html Why we have to import a library, what is so difficult?

Thanks.

I do not have the first two sensors.

“Why we have to import a library”
To make the sensor readable by the Arduino

Your computer uses a mouse.
Why does your computer need a mouse driver?

Why we have to import a library, what is so difficult?

In this case, you don't. It is not difficult to write the few lines of program required to read the DHT11. But someone else already did, so why not use their code?