Can anybody please tell how the learning bosses thing work?
It's merely a flag for when looking at the Raid Analysis and Current Standings you can see who attends the Learning (aka "New" or "Not farm status") encounters, versus those who only attend raids that are on farm status.
Is this a way to increase or decrease the amounts awarded at an encounter untill a boss is considered as on farm ?
Not in any sort of automated mechanism. For encounters like that, you just change the value of the boss on the upload by entering a different number in the "Point Value" box.
Also - today I can set the % on how much dkp each rank in the guild should be awarded - but is there some way to set different amounts of dkp for farming bosses, never killed before bosses etc.
This would be awsome because we award a bonus when a boss is killed the first time - but we would also like to decrease the amount awared for a farming boss.
My guild actually did the same thing for a long time. But given the rarity of "new boss kills" (ie, one to three a week), manually tweaking the cost when uploading and putting in the comment of "First Kill" was trivial enough.