This is how you make somewhat realistic fire in GIMP
Step 1: Click "New"
Step 2: Set Width to 2000 and Height to 1800
Step 3: Click on Filters>Render>Clouds>Difference Clouds
Step 4: Check the Box Next to "Turbulent" Then Click OK
Step 5: Select "Curves" Under the "Colors" Tab
Step 6: Move the Curve So It Looks Like This, Then Click "OK"
Step 7: Under Colors, Click "Color Balance"
Step 8: Click on Shadows, and Set the "Cyan>Red" Bar to 100 and the "Yellow>Blue" Bar to -100
Step 9: Do the Same With the "Midtones" and "Highlights" Tabs Until the Picture Looks Like This
Step 10: Use Any Select Tool, Select a Section of the Picture, and Copy It (CTRL+C)
Step 11: Go to the Image You Want to Paste It On, Click "New Layer," and Paste It In.
Step 12: Use the Move, Rotate, and Scale Tools to Move the Selection As You Wish. Once Done, Deselect.
Step 13: Equip the Smudge Tool and Set the Size As You Wish. (Reccomendation: 160)
Step 14: Make Little Strokes in the Fire Pattern Going From Bottom to Top.
Step 15: Continue Until Your "fire" Looks Somewhat Realistic.