This tutorial shows you how to model a bottle in Blender

3°) Improve the bottle

Add any loop  ( ctrl R ) with the wheel of your mouse, you can add several at once

( look at the pictures below)

In MODE OBJET apply the modifier

Go face mode, select any face in the middle of the bottle and press E to extrude the face

 reduced the surface ( S ) and down slightly to the inside

  Tutorial following : Make a bottle (4) make a template