Gimp 101

Use the pen tool for most selections

Path tool Ctrl click final (first) point to close

You can make a selection from the path here

Or here ...

Note: all windows/palettes under dialogs

Hide the active path with the eye

Here are some selection options

A feathered fill of 20,

on a transparent layer,

deselected:

How to get the selection back?

Alpha to selection

Ctrl K = delete (clear)

To scale down select

Make a new path and stroke

or ...

If you don’t want to see the pen points

after you just made a path

Exit the pen tool

 to

otherwise, use the eye on paths

Keep aspect ratio when scaling

Hit the scale button when it looks right

You will still be in the scale tool,

so go back to move

to re-position

Under Tools

Document history is nice

Undo history

Brushes

Clone stamping

Ctrl click is your sample method

Make a channel from selection

Select via Layer/Transparency/Alpha to selection

then go Select/Save to channel