This would be my longest write up so far but I do not think I can do it justice so will suggest that people take a few minutes to read the links that have very extensive detail on this holiday.
Nowruz is the new year day for the lands of the former Persian Empire. From what I have found this could be the oldest holiday celebrated though none of my sources said this. They do point to this having been around for at least 3000 years and is still a very important day in many counties most notably Iran, home to the origins of the Persian Empire.
Like many days recognizing the new year many of the traditions sound the rebirth and in fact the day is set by the spring equinox so there is the combination of both new year and beginning of spring. People will clean out their houses and buy new clothes for the year to be worn on the day. Also it is traditional to visit others in their houses with preference given to the oldest member of the family then making the way down to friends. Similar to the idea in the west of what you do on New Years Day will be what you do the rest of the year, a happy day means a good year while fights indicate a year ending badly.
I wish I could take more time but just can not at the moment so please take a look at some of these links.