Here's a step-by-step guide on how to make a trap beat:
1. Start with the drums. Trap beats sit around 140BPM - set your tempo accordingly. The 'Studio Trap' kit that comes with Serato Studio is going to be the perfect kit for your beat. Select the 'Make Beats' button to generate a beat, selecting the trap genre. Add/remove notes until you're happy with it.
2. Add an instrument. Typically trap beats have a lot of piano sounds and sparkly melodies.
3. Add a bassline. Let's fatten up our track by adding an 808 bass (the '808 Knock Bass' in Serato Studio works great).
4. Structure your beat.
5. Arrange it.
6. Master it.