At this point you will no longer see the horizontal drainpipes and the main sewer line but you will see the stubs that extend vertically out of the sand.
How to plumb shower drain in concrete floor.
The first step is to decide on the schematics of the shower base and ordering it.
Later if an old drain line ruptures or the homeowner puts an addition onto the house it might be necessary to cut the concrete floor to reach the old plumbing or to connect a new line.
How to install a shower drain in the concrete floor.
If you ever asked this question before then start by planning the execution of this job.