Not an easy subject at all. This is a quick tute based on memory, cos I am at work, so don’t have Blender here to check everything.
Basically, to do something like a laser, you need to separate your model into two layers: one with just the beam, and one for everything else. Light the rest of the image normally, but either give the beam a few lights set to a single layer, or set its material to emit light.
Now you go to the rendering buttons and set up two ‘renderlayers’, one for the laser beam and one for everything else. If you then click the ‘single’ button next to the renderlayer, and render, you will see that if you render one renderlayr, you will see only the laser beam, and if you render the other you will get the rest of the image.
If you get that far, you are half way there.
Now open a nodes window and ‘add’ two input devices. Set one to input renderlayer 1, and one to input renderlayer 2. Now add a ‘mix’ object, and connect the outputs of the input devices to the inputs on the mix device. Now add an output device ( render output )
Turn off the ‘single’ button in the rendering, and set ‘do composite’ and you should now see both the laser beam and the rest of the scene.
Open an image ediitor window and set the view to be ‘render output’, so you can see the node editing in real time.
Now break the connection between the ‘beam’ renderlayer and the mix. Add a blur device, two multiply devices, a RGB curve device and another mix device. Chain them together so the image of the laser beam is sent to the RGB curve, so you can edit the colour. Now send that output to the blur device and then to a multiply device (I think they are actually called ‘maths’ devices, actually, but you can pick multiply from a menu). Take another line from the RGB output to the multiply device, and then mix the results of your multiplies back together. Take the output of that back to the input of the mix that you started with. You are now taking the image of the laser beam and tweaking it to give a nice red or green ( or whatever) flash. You then blur this to get your ‘glow’ effect, and multiply it by maybe 2 or three to make it bright and cause it to flare slightly. Now you add to it a non-blurred copy, once again multiplied to make it flare really brightly. Finally you add these back to the original.
A good trick when doing this is to add a ‘viewer’ device, and attach this to whatever part of the chain you are tweaking, an set the image viewer windo to see the output of that viewer, from the drop down at the bottom of the window. This allows you to see each part of the image that you are building.
Once you have done this, you just tewak how much of each of the three images are mixed together with the ‘mix’ devices, and you are done.
Sounds complex, I’m afraid, but once you have got he gist of input and output devices in the node editor, the rest is just playing around with the other nodes until you get what you want.