I know the thumbnail says 14w21b. I'll update it soon
REMEMBER SNAPSHOTS ARE UNSTABLE AND CAN CORUPT YOUR WORLDS. BACKUP YOUR WORLDS BEFORE USING SNAPSHOTS.
Step 1:Launch Minecraft Launcher but DO NOT CLICK PLAY!
Step 2:Click the New Profile button that is in the bottom left corner of the launcher
Step 3:When the New Profile window opens Set Name Profile to something you will recognize as the snapshot profile. (I usually use snapshot)
Step 4:In the Version selection section, Tick Enable use of experimental development versions ("snapshots")
Step 5:Select the snapshot you want in Version dropdown menu.
Step 6:Click save profile and select it in the launcher
Step 7:In the bottom right corner of the launcher check that it says ready to download and play (if you've already downloaded it will just say play)  minecraft (snapshot you chose)
Step 8:Click Play and GO!!!