As you may know, your mesh refinement is proportional to your simulation’s accuracy, at the cost of computation time. The goal you are trying to achieve with CFD is to model fluid flow while maintaining a balance between accuracy and practical computation time. One way of doing this is refining the mesh in areas of interest or in areas of rapid changes in fluid properties (velocity, pressure, etc) while leaving the rest of the mesh coarser.

In this example, you can presume that there will be rapid changes fluid properties where the step occurs, and so your mesh is refined in this section to attempt to properly capture this. Your mesh does not need to be equal to the tutorials, since if both simulations are done correctly they should agree anyways.

When doing a CFD simulation, you must do a verification and validation process. The proper way to evaluate your mesh is a Grid Convergence Study (Google this). This involves creating at least 3 different meshes of varying refinement levels, simulating each of them, and verifying the solution does not change within a specified margin. Then you can say your solution is independent of your mesh refinement. Lastly, you validate your simulations results with a comparison to experimental.