Probably really simple answer, but I can't seem to find any info about how to make a face concave.
Another way you can do this is with Proportional Editing (O):
Steps taken in the gif
- Add a cylinder (⇧ ShiftA> Mesh > Cylinder)
- Enter Edit Mode (↹ Tab)
- Select the top and bottom faces (⎈ Ctrl↹ Tab> Face to set the selection mode, then ⇧ Shift RMB to select)
- Inset (I)
- Select just the top face and inset again (I)
- Add loopcuts (⎈ CtrlR, then MW to adjust number of cuts)
- Select the middle ngon
- Turn on Proportional Editing (O) and set the falloff type in the header
- Move the face down on the Z axis (G, Z. Use MW to adjust the falloff)
- Add a subsurf modifier (⎈ Ctrl1, where 1 refers to the number of subdivisions in the modifier. Can be any digit from 1 to 5)
- Add supporting loopcuts (⎈ CtrlR) to control the subsurf.
Add a Cylinder with NGon cap fill type. Select the upper edge loop with Alt+RMB, then press Ctrl+B to bevel it. Set the bevel Segments number as desired. Next select the edge loop as pictured below, snap the cursor to it (Shift+S-->Cursor to Selected), select the other edge loops towards the top and press S, Z, -1. Add some loop cuts with Ctrl+R to sharpen the edges (if you wish to add a Subsurf Modifier in the next step).