How to Assign one way and two way slab in ETAB & Model Flat Slab with drop panel

ETABS, developed by Computers and Structures Inc. is a powerful 3D finite element software for the design and analysis of buildings. It provides Structural Engineers with a powerful tool to model both simple and very complex structures. The user has the flexibility to design “stick” or “frame” elements (such as beams or columns). There is also ability to model shells or membranes for slab and wall elements. But what’s the difference between a shell vs. membrane element? and which one should you use in ETABS?
The flat slab is a two-way reinforced concrete slab that usually does not have beams and girders, and the loads are transferred directly to the supporting concrete columns. ETABS automates several slab and mat design tasks