Install a file archiver like 7-Zip or WinRAR
Open Minecraft Java Edition and locate the resource packs folder
Create a new folder for your texture pack
Add a pack.mcmeta file to the folder
Set the pack format in pack.mcmeta for your Minecraft version
Create an assets folder inside the pack folder
Inside assets, create a minecraft folder
Inside minecraft, create a textures folder
Copy the vanilla texture files you want to edit from the game files
Edit the copied PNG files in an image editor
Keep the same file names and folder structure
Save all edited textures as PNG files
Add any custom sounds, models, or language files if needed
Zip the pack folder if required
Place the pack folder or zip file into the resource packs folder
Open Minecraft and go to Options
Open Resource Packs
Move your pack to the selected list
Apply the pack
Test the textures in game
Fix any missing or incorrect files
Repeat editing and testing until finished