Adding Slingshot And Show Desktop To Plank

Slingshot is normally started by clicking Applications in the top panel, but you can add a starter in Plank as well :

sudo nano /usr/share/applications/slingshot.desktop

paste the following lines :

[Desktop Entry] 
Version=1.0 
Type=Application 
Name=Slingshot 
Comment= 
Exec=slingshot-launcher 
Icon=plank 
Path= 
Terminal=false 
StartupNotify=false

Save and close.
See : https://answers.launchpad.net/slingshot/+question/224173

Alternative icon for the launcher : http://jivebs.deviantart.com/art/Custom-Slingshot-launcher-Icons-392727962

In Files navigate to /usr/share/applications and drag the Slingshot icon to Plank and release when seeing a + sign....

For adding Show Desktop  open System Settings > Tweaks > Plank > Show Desktop Icon.