What about filters and?

Am a little confuse, I want to buy an and filter for day long exposure photography, but I see that some filters that screw into the lens and others are like mirrors (p COKIN SERIES) What should I buy? My lens is a 67mm nikon 18 105 vr Thanks

Added (1). 67 is the sizes of the cap lens

Just go for 67mm screw-in and filters with your wanted stop reduction. If you are going to do long exposure photographs in daylight you need 7-11 stops and

You have another option - the Cokin system.
They are square filters in a holder. It makes no difference compared to the screw in for a normal and filter, but is much better for graduated and filters because you have total control over the placement of the filter. In a screw-in grad and you can only choose the angle of the horizon, but you can't choose how far up or down in your shot it is.

The Cokin system is also good for stacking filters.