Ok Roosta, here we go.
"Most" landscape photographers use filters, there are screw on ones and ones that require a filter holder, the latter being the most practical so most common. These filters come in a number of different types, NDx( neutral Density) x being a number, which usually relates to the number of f stops that the filter reduces the amount of light entering the lens eg ND2 = a neutral Density filter that will reduce the light by 2 f stops. this allows you to use longer exposures, useful for catching that smooth water movement effect.
Then we have GNDx( Graduated Neutral Density)x as above. These filters have a dark portion that you can use to cut the amount of light in a specific area of the scene, typically used with sunrises. These come in GND hard and soft(amongst others) soft being a very gradual lightening of the filter, hard being a definite stop across the filter.
they also come in various colours.
Have a look at some of the suppliers sites listed below and you'll get the idea
http://www.cokin.fr/
http://www.leefilters.com/camera/pro...46C9C1B6AA3DD/
http://www.singh-ray.com/grndgrads.html
not the complete answer on filters but it will get you started.
Have fun