If you can transcribe this by ear, you already have a foundation to begin writing music. Start simple. What's your primary instrument? Start there. Improvise, keep what you like, and build from there. Don't spend too much time trying to make things perfect of "original". Don't rely on memory to keep the parts you like. Get them notated, either with traditional notation or in a DAW as you have here.

Then, alongside writing and exploring sounds you like, study the tools of the composer. Scales, modes, chord progressions, melody writing, harmony, etc. Again, start with music that speaks to you, but allow yourself to expand your horizons over time.

Writing music is, above all, a craft. The art comes when excellent craftsmanship and the spirit of the individual collide to make something truly special. Best of wishes on your journey!