Accompaniment is actually an arrangement. In addition to using the correct chords according to the melody, we should also know the arrangement method of musical instruments, that is, what instruments will produce what effects when used. You should know that all these things can be done through study. Besides these, the most important thing is to have your own style, so that the arrangement of these instruments can reflect the ideas you want to express!
Professional arranger software includes sonar, nuendo, cubaes, etc. It is essential to master these softwares with professional knowledge. In addition, there is another method that can be recommended to beginners, that is, using automatic accompaniment software!
You can find an automatic accompaniment software called band in the box. If you can use it flexibly, others will generally not hear it.
If you want to arrange music, you need to know: interval, tonality, chord, orchestration, music style, MIDI production, soft sound source, effect device and so on. A pair of sensitive ears is also essential.