There are two places where you can add new desktop entry files depending on whether the launcher icon should be available for all users or only a single user.
For example, to create a launcher for the eclipse IDE:
Global (all users) -
/usr/share/applications/eclipse.desktop
Local (single user) -
/home/myusername/.local/share/applications/eclipse.desktop
Assuming that eclipse is installed to /opt/eclipse, the eclipse.desktop file would look something like this:
[Desktop Entry]
Name=eclipse
Type=Application
Categories=Development
Exec=/opt/eclipse/eclipse
Icon=/opt/eclipse/icon.xpm
Terminal=false
Hope this helps!