Ok.
This is going to get kinda complicated, so best grab yourself a coffee.
What you're going to need, is Minecraft, the mod you want, and WinRAR.
Now, what you do is extract the usable files from the mod folder. It might be a .zip format.
Then, you navigate into your Minecraft folder, to the bin folder, then RIGHT CLICK on Minecraft.jar. Select Open With: WinRAR.
This should expand the contents of Minecraft.jar into the WinRAR window.
Then, you DRAG AND DROP the files from the mod folder, into the expanded Minecraft.jar.
WinRAR will say something about overwriting files most likely, so just click yes, i want to make changes.
Then, once all the files are into Minecraft.jar, you can close that window.
Next, start up your Minecraft game. The mod should be installed.
Post back if it worked or not