why does my glass look so strange especially when smooth shaded

Question

Here's what it looks like flat shaded, in cycles, with the settings. i only upped transmission to 1 and roughness down:

Here's what it looks like smooth shaded in cycles:

Answer 1

It looks like maybe your normals are flipped. Check this box.

If your glass looks like this -

Enter Edit Mode, select all with A, press Alt + N and select Recalculate Outside.

Your glass should look a bit better, but it looks to me like you should consider adding some supporting geometry on the top and bottom.