In GIMP, background removal is usually done by making an accurate selection of the subject, then masking or deleting the background. The exact method depends heavily on the image:

• For simple images, use GIMP’s selection tools carefully. Good selections are the key to good cutouts.
• Refine the edge with tools like feathering so the subject doesn’t look unnaturally cut out.
• For complex subjects—like hair against a detailed background—there isn’t one easy recipe. It often requires more advanced isolation techniques and careful manual work.

If the background is mostly one distinct color, a quick method is:

1. Open the image.
2. Go to Select > By Color.
3. Click the background to select it.
4. Use Colors > Color to Alpha to make that color transparent.
5. If needed, press Delete after selecting the background.

This simple approach works best when the background color is fairly uniform and clearly different from the subject. For anything more complicated, expect to rely on selection, masks, and edge refinement rather than a one-click solution.