As was mentioned in a comment, your original problem was that proportional editing was on, and so nearby vertices, beyond those you had selected, were also being affected by the resize operation. To fix this, you can toggle out of proportional edit with o or click the associated icon.
Your next problem is probably a result of an extra extrusion. If you extrude with e and then think better of it and click Esc, it will appear as if the extrusion operation has been aborted, but it hasn't. You've extruded the face with some zero-width edges connecting the visible edges of your cylinder to the face. When you resize the top face, those zero-width edges are stretched, leaving the visible edges unaffected and making the top look like a flate plate or disc.
Fixing this can be a little tough, but try the following:
- Undo any resize of the top, so it looks like the original cylinder.
- Make sure the object is selected and you're in edit mode.
- Select all the geometry with a.
- Perform a "merge" with m and select the bottom option "By Distance" from the pop-up.
- You should see a note in the status bar at the bottom that says "Removed xx vertices". This means those zero-length edges were removed and their vertices merged together.
- Now, if you select the top face and resize, it will hopefully work as intended.
If that still doesn't work, you might want to just delete the cylinder object and try it again from the beginning.
