How do I build a basketball court with textured mat?

Did you already purchase the mats? If so, they should have recommendations on surface preparation. I would secure the dirt with paver stones equal length and width apart, add dirt, level and compact the surface, and add a slight slope for drainage.

The basketball courts with textured mats that I have seen have all started with a concrete slab or wooden base then the mat for a perfectly smooth finish.

You will want to level the surface. It would be best to kill out the grass too so it doesn't grow up through your mat.