Above in picture form

Difference between normal light and laser light -

http://www.colorado.edu/physics/2000/lasers/index.html

LASER stands for -

Light
Amplified by the
Stimulated
Emission of
Radiation

Focused means focusing the beam into a point, focusing is good for burning.

Collimated means keeping the beam straight for as long a distance as possible and not focused into a point. This is good for long distance

Combining Lasers Beams-

A cubed beam splitter is used for joining two beams of the same frequency -

A dichro is used for joining two beams of different frequency -

Visibility