I don't have a MOXF6 or MOXF8, but since you say the manual is confusing to you, I'll take a stab at it. Keep in mind that I can't actually follow these steps myself, since I don't have one of these keyboards-- I'm just trying to simplify the instructions in the manual for you.
Press the [SONG] button.
Select an empty Song.
Set the desired time signature.
Press the [REC] button.
Press the [F1] SETUP button.
Set "Type" to "replace" (for Realtime Recording).
Press the [F2] VOICE button.
Press the [CATEGORY SEARCH] button.
Select the desired Voice.
Press the [REC] button.
Press the [|<] (Top) button to go to the top of the Song.
Press the [>] (Play) button to start recording.
Play the notes you want to record.
Press the [.] (Stop) button to stop recording.
To hear what you recorded:
Press the [|<] (Top) button.
Press the [>] (Play) button.
I hope this helps!