Slingshot is the default elementaryOS application launcher in the top left corner of your screen. Since elementaryOS doesn't come with an editor to change or add menu entries in slingshot by default, here's how to do it!
First, we are going to install alacarte. That's the default menu editor for Gnome, but with the right modifications we can also make it work on elementary.
Open up a terminal and type:
sudo apt-get install --no-install-recommends alacarte
The '--no-install-recommends' option makes sure you don't install the gnome environment which you don't need to have alacarte running.
Now, we're going to make alacarte work with slingshot. Type this in a terminal:
sudo scratch-text-editor /usr/share/alacarte/Alacarte/MenuEditor.py
This will open up a text file. Hit ctrl+F to search for 'applications.menu' and replace all with 'pantheon-applications.menu' (you have to replace applications.menu twice in the file). When done, close the file.
Now start the menu editor by typing 'alacarte' in slingshot or in a terminal:
|Alacarte up and running|
That's it! You can now start adding applications and changing them (icons, command prompt...) so Slingshot looks exactly as you like it. Have fun!