I make texture packs, but it took quite a while to get started. One of the smplest ways to it is to find a texture pack that's extremely similar to the default, packs that changes a few mobs are recommended(make sure you change what's changed, if not you're stealing!)
If you do this you won't need to use winrar or whatever file opening thing, you know. When you've got that set, you'll need to get an image editing/painting program that tackles transparency.
(I use Gimp, Microsoft Paint is NOT recommended)
When you've found the files you want to change, open them in the editing program, and start doing whatever you want.
The file names are often obvious, but not always. (mooshrooms are called redcow in the files)

To use the texture pack you've made, follow these steps carefully:
1. Put all the changed files into the desktop
2. Put mobs into a folder named ''mob'' and armor in a folder named ''armor'' etc (make a folder with the same names as those you found the files in and make sure you type correctly)
3. Make a zipped folder
4. Put all the folders into the zip(terrain and pack png must not be in a folder, and make sure you don't copy-paste them, 'cause that won't work)
5. Open minecraft(obviously)
6. Click on the texture pack button and choose ''open texture pack folder''
7. Find the texture pack file you made, looking at the desktop is recommended
8. Copy-paste the texture pack into the texture pack folder in minecraft, like with downloaded packs.


After proper testing and taking screenshots, upload it at PMC and give me credit for tutorial.