When you install it, make sure it's being installed into your Vstplugins folder. Cubase will automatically recognise it when it starts up and it will be available in your VST Instruments list.
(Alternatively, if you want to install it elsewhere, you need to make sure you point Cubase to this folder... it is often called the Shared VST Folder because the idea is it lets you use VSTs that are installed for use with other applications and therefore are installed in a different place.
To do this, click on Devices/Plugin Information and then click the Choose button and navigate to the Shared folder)
To use the instrument, click on Devices/VST Instruments and a box comes up. Click where it says "No VST Instrument" and a list of your installed VST instruments pops up. Click on one to use it (eg. LM7)
Now you have the LM7 ready to use as VST instrument number 1.
To edit the sounds it poduces, click on the e below the "on/off" button in the VST Instruments box. It will open the GUI for the instrument.
Once you are happy with the sounds you want it to produce, go back to the main Cubase screen and choose which track you want to use the instrument. Click on the 'out' box in the track panel and choose LM7 (or whatever you chose as the instrument) as the output.
If you can't see the 'out' box, do it this way... in the left hand panel for the chosen track, click on the bottom tab which is "channel" and you'll see a slider. Underneath the slider you will see the instrument name and under that the chosen output (says "Not Connected" by default). Click on where it says "not connected" and choose the instrument you want it to output to. The chosen track will now play through the chosen VST instrument.
Remember you must have the instrument available before you can use it with a track so you must make sure it's loaded into your VST Instruments first.