1.Compose a song professionally: It's really long if i have to talk about every device and detail. I'll share a link to give a heads up in a wider range. Briefly, if you want to compose a song professionally. "I. You must get a deal with studios-record labels. Doing that, you must represent yourself as musician, singer or band and come up with few samples of your music work and earn their trusts to give you professional tools". "II.You must be rich and educated enough to create a professional studio on your own". "III.You must rent a studio.
2.Composing normally and for fun: "I.You can use many available software out there such as FL Studio." "II.You can buy different instruments or gather with others and play along, record your instruments on small gear of recording equipment"
Here's the link regarded the studio requirements in different aspects.
Example of studios and professional equipment.
3. "I. Tuning instruments are clear. When you get around each instrument you are interested in, you'll learn how to do it. "II.Tuning soundtrack for timbering, balancing, rising or lowering different concepts of the song or each instrument individually throughout the track you must use recording equipment. When you are recording, whether a small kit or professional gear. There are tuning options and tools which you must get educated of how you can use them also gain experience by it. It's not a very easy job. Even musicians are clear about what they want and know what they do, yet they use experience of a producer to help them to bring the best out of their records.
4.For knowing guitar chords or in general music chords, you must study the music. And when you want to go further on a specific instrument, you must specifically study the function of the instrument and practice constantly. For instance, music basically get around mains keys: DO RE MI FA SOL LA SI - C D E F G A B - these are keys of guitar as well.