DTM stands for desktop music, a way of making music in which composing, recording, editing, and mixing all happen on a computer or tablet. It is a widely used term in Japan, and it refers not to any particular software but to the whole activity and setup of producing with a computer.
What you can do with DTM
You can carry a song all the way through: MIDI programming, recording vocals and instruments, placing loops, sound design, mixing, and mastering. And not only at home, since you can take a laptop out and work anywhere.
The DAW at the center
The DAW is what sits at the center of the process. On its screen you lay out tracks, play software instruments, and edit audio and MIDI. DTM is the overall method; the DAW is the central piece of software for it.
The gear you need
The minimum is a computer or tablet, a DAW, and headphones. Add an audio interface if you want to record microphones or guitar, and a MIDI keyboard if you want programming and playing to be easier. Building up gradually as your needs grow is perfectly fine.
You can start without playing an instrument
Because you enter notes in the piano roll and can fix timing, pitch, and length afterwards, you do not need advanced playing skills. That said, having a keyboard speeds up auditioning sounds and entering phrases. How to choose a keyboard for DTM (Japanese) covers this in more detail.
How to think about getting started
Rather than buying a pile of gear and plugins up front, pick the DAW you want to use and finish a short song, and you will learn the controls faster. How to think about a computer for DTM (Japanese) may help when choosing your setup, alongside checking current product specifications.
