The (English) Gimp help is https://docs.gimp.org/2.10/en/gimp-tool-gradient.html
The basic gradient is foreground color (FG) to background color (BG) Set those colors in the toolbox color selectors by click in the icons.
There is also in the Gradient Tool Options various forms for FG to BG use (RGB) also lots of premade gradients.
Draw the gradient into the selection. There are control points in the line joining start and finish. Add more by clicking on the line.
Hit the enter key to complete using the Gradient Tool.
To finish using a selection use Select -> None
A short animation of that procedure: https://i.imgur.com/vqNXgja.mp4
The basic gradient is foreground color (FG) to background color (BG) Set those colors in the toolbox color selectors by click in the icons.
There is also in the Gradient Tool Options various forms for FG to BG use (RGB) also lots of premade gradients.
Draw the gradient into the selection. There are control points in the line joining start and finish. Add more by clicking on the line.
Hit the enter key to complete using the Gradient Tool.
Quote: how do I get rid of dashed lines around the selected area? Escape button doesnt work
To finish using a selection use Select -> None
A short animation of that procedure: https://i.imgur.com/vqNXgja.mp4