the part where it is thirds in the right hand and seconds(?) in the left hand, I don`t understand how it is supposed to fit together, and in recordings, it is to fast to make out... help?

sam, are you talking about the first Arabesque by Debussy, the one in E major, that begins with Andantino con moto? I see the 3-against-2 you`re describing, starting in the 6th measure (in the edition I`ve got).

heheh, unless you mean some other arabesque.

yes, that`s the piece, how can you learn to play that fast? Do you have to play in a sequence of six, because it doesn`t sound like it on the recording I`ve got?

At tempo, the sequence of six you`ve described would not be really audible. But if I understand you correctly, that is a real good way to learn how to do it. When I understood it while doing it slow, what I learned made sense. Before I understood it, I couldn`t even do it slow.

Once I grasped how 3-against-2 is correctly played, I was able to speed it up. It works the same way for any other polyrhythm, too, even snarly-looking ones. Others I am working on at the moment are 5-against-2, 7-against-2 and 11-against-6, all in Chopin Nocturnes.

I`m looking at measure #6 again of the Arabesque and the clearest "sequence of 6" I can see would be the last two sets of triplets. But lemme break this out another way, looking at the whole measure: on the treble clef there`s a quarter rest, then three sets of 8thnote triplets. Each of those sets of triplets has to fit into one beat. In the bass clef in measure 6, there are only 8thnotes: they go "1 & 2 & 3 & 4 &". That`s a way of "saying" the rhythm of what the LH (left hand) is doing. The thing is, how to get those triplets in there, played correctly as triplets, in the same 4 beats.

The "sound-alike" I was taught for triplets is "pineapple." The rhythm sound of each triplet is like saying pineapple once. In measure 6 there`s a one-beat rest, then "pineapple pineapple pineapple."

During that one-beat rest, the LH plays "1 &."
During the 1st pineapple, the LH plays "2 &."
During the 2nd pineapple, the LH plays "3 &."
During the 3rd pineapple, the LH plays "4 &."

Step 1. Tap the fingers of your LH on a tabletop in the rhythm "1 & 2 & 3 & 4 &". Keep it steady and even.
Step 2. Keep doing that, and say "pineapple" during the "1 &" so that it takes the same time to say it as it takes to tap your LH fingers "1 &."
Step 3. Keep tapping, and now say four pineapples for each complete "1 & 2 & 3 & 4 &." When you can do this, you know what the 3-against-2 polyrhythm sounds like and even what it feels like.
Step 4. Let the LH rest. Now if you can tap the fingers of your right hand on a tabletop in time with saying pineapple (tap-tap-tap, tap-tap-tap) you`ve shown your RH how to do the triplet rhythm.
Step 5. Resume the LH tapping "1 & 2 & 3 & 4 &" -- and then start the RH tapping the pineapples.

big hint: the second note of each triplet should be heard between each pair of 8thnotes. If it isn`t, the polyrhythm isn`t even and what you`re playing is something different.

It sounds stupid but it`s really useful in understanding how this polyrhythm thing works: Words (or phrases) that have the same number of syllables as the figures in the polyrhythm are a good way into it.
Since I need more fruit in my diet, I like "pineapple" for triplets. Somebody else I know prefers to say "underwear, underwear, underwear."

Once you can do a single 3-against-2 accurately, then you can do as many of them as the score calls for, as fast as you like.