Ok guys! I'm gonna teach you how to mod!
Ok this part is for windows.
Step 1. Find the mod you want.
Step 2. In the start window type in %appdata% and click Roaming, after you click Roaming click .minecraft
Step 3. After you click .minecraft click on bin and then right click minecraft.jar and open it with WinRAR or 7zip (Which ever one you have) ALSO : Delete the META-INF If you don't minecraft will crash and you'll have to force update it
Step 4. Open up the mod you downloaded and drag it to the minecraft.jar and close it. Now your ready to have more fun! *Note* Most mods require modloader make sure you have that installed too

Now for Mac: Its a little bit harder type in the lines I tell you to type (or just copy and paste)
Step 1. Open up terminal.
Step 2. Type this in terminal
cd~
mkdir mctmp
cd mctmp
jar xf ~/Library/Application Support/minecraft/bin/minecraft.jar

Go outside of terminal and click the folder with the mod and drag all the files into terminal (do NOT hit enter)
Type or copy and paste the following rest

fm META-INF/MOJANG_C.*
jar uf ~/Library/Application Support/minecraft/bin/minecraft.jar ./
cd ..
rm -rf mctmp
Hit enter and run minecraft! Enjoy new minecrafters! This is the end of my tutorial and I did NOT copy and paste this it took me a REALLY long time :P Thank you guys!