The two ways to learn to play a keyboard instrument whether it is the organ, piano, or one of those 61 keys or more electronic instruments is either by ear or by note. It all depends on how you're wired. A person who sees visually and learns by listening finds it easy to learn to play by ear. A person who has to see the words in front of him, has a good verbal memory, finds it easy to learn to play by note. People who write below a chord, the names of the notes that they have difficulty with, usually find it easier to play by note. A person who is better learning by ear finds that writing the notes gets in the way. Consequently if a person who plays by ear, plays the chord on the organ and tells the person who plays by note to play it like it sounds, the latter will have difficulty. It's all a matter of how God made you and you have to compensate for this.
This simply means hearing a musical competition and being able to play it on the organ, piano, guitar, or whatever instrument you are familiar with. So before you can play by ear, you have to try out the different keys on your instrument until you can associate the sounds. Now once you associate the sounds, you then try playing the tunes you are most familiar with. It also helps for you to do scales and exercises. What I mean is that unless you are familiar with how the note sounds you cannot play by ear.
This is the opposite of Playing by Ear. You have to see the written piece before you. It's how most music lessons are taught. You see middle F, for example, not by its sound, but its location on the staff paper. You associate each set of notes by what it looks like, not by what it sounds like. When you memorize a piece, you don't think of what it sounds like, but what it looks like on the paper.
Although you find it easy to learn by one method, you can use the other method to learn pieces that have greater difficulty or some tune or melody you never heard of. For instance, if you played by ear, you can now associate the tune, Merrily we roll along with the notes e-d-d-d-e-e-e, and you'll know that e is across the first staff, d just below the first staff, c, below d and has a short line through it and so on, so that when you come to an unfamiliar tune or song such as the Ghanian National Anthem, you can visualize how it sounds by what it looks like. So in the end, you might combine both methods, but I still prefer playing by ear. I can pick up many tunes that way, but my practicing chords and practices for the left hand, makes it easy to play the accompaignment.
This is seeing the notes, treble clef, base clef, whether the notes are in quarter time, how they are arranged and being able to play the piece even though it is the first time you ever saw the piece. Before this, however, you learned where, for example, High D flat was on the staff, how long to hold an eighth note, how to play stacatto, the E scale both ways, what happens when you join four black notes together with a line on top, etc. You also had to write in that little book with the staff paper, what a half note looked like, where is the middle E, etc. and after you have done this for a time, you can then go to the store buy a copy of "Pieces for the Piano or Keyboard", play one of the pieces, and at the same time, look ahead because you've been prepared.
This is playing the piece in a different key from what it is written. It can be done for many reasons. You may be a beginnner or have not learned what key has five flats or four sharps. You may be playing for a singer who cannot reach the range of the original piece. For instance if the singer happens to be a contralto, she cannot reach the highest C or if the singer is a soprano she might find it difficult to go much below the middle C. Therefore in the first case, if the piece was in F, it would be best to transpose it to C and in the second case, it would be the reverse. Once you learn scales and chords, note and or playing by ear, tranposing becomes easy.
A cavaet: I have no idea whether there is a music book with the title of 'Pieces for the Piano or Keyboard' so don't ask me where you can buy it.
By the way, since most of the Hammond Spinet organs were no longer made after the 1970s and most of the music books are of that period, it would be good to learn to play by ear so you can play any of the musical compositions after that period. You could also use the EZ Keyboard or Keyboard books. You could use the other organ books, but Spinet organs have a small keyboard. I'll have to look for some organ book links.