How to change the texture of Vanilla blocks

So, in my mod, I'm adding better water textures. I've found the texture I'm gonna use already, so I heard that all you do is go into the Source folder and then Main...etc, and then in the same folder that says the name of your mod, in this case "The Minecraft Anime Mod", I put a folder called "minecraft" there. Not inside of "The Minecraft Anime Mod", just next to it. Then I added various folders like assets, textures, blocks and then added the water textures in. I added one for the still movement of water, the flowing movement, everything! Yet it did not work. I loaded up the test Minecraft and the textures were the exact same. I looked up a YouTube tutorial, a confusing one might I add, and I believe that he did the same thing as me, so I'm not sure what I did wrong. Do I somehow have a folder in the wrong place? Please help, thanks!