Can anyone suggest a software to draw 3D diagrams of cells, DNA etc? I have been trying to use 3D Max but I feel it is not user friendly (or maybe I am so ignorant with the software!)
It depends on what/how you are wanting to model 3D objects. If you are wanting to do 3D animation or to deform complex meshes, you will probably want to stick with software like 3D Studio Max or Blender (or the option suggested above).
If you are wanting to model simple geometric shapes, and (potentially) 3D print the models, you would be best going with a solid modeller such as Auto CAD or PTC Creo. The latter offers a free version, as well as educational versions (link below).