Ketiva VeChatima Tova

[may you be] written and inscribed/sealed [for a good new year i.e. by God]

Rosh Hashanah (Hebrew: ראש השנה‎, literally "head [of] the year"), is the Jewish New Year

Shofar or Ram's Horn Instrument use at Rosh Hashanah

There are three important stages in the spiritual order of the Ten Days of Repentance (the ten days between Rosh Hashanah and Yom Kippur) unfolds: On Rosh Hashanah God "'opens' the 'books' of judgment" of creation and all mankind starting from each individual person, and in those books it is first "written" what will be decreed, hence the emphasis on the "ketiva" ("writing"). The "judgement" is then "pending" and prayers and repentance are required. 

Then on Yom Kippur, the judgment is "sealed" or confirmed (i.e. by the Heavenly Court), hence the emphasis is on the word "chatima" ("sealed"). But the Heavenly verdict is still not final because there is still an additional chance and positive expectation that until Sukkot concludes there is hope that God will deliver a final good and favorable judgment, hence the use of "gmar" ("end") that is "tov" ("good").

Adapted from Wikipedia

As I understand it the High Holy Days are the most important days of the Jewish Religious Calendar just as Ramadan (just finished) is for Muslims and Christmas and Easter are for Christians.   I always made it a point to point this out to my students so that they would not make the cultural error of equating Hanukkah which usually occurs around Christmas and involves the giving of presents as a major holiday. I also used it as a kick off point for a lesson about calendars. 

Rosh Hashanah begins at sundown today (All Jewish Holidays begin at sundown and ends at sundown the following day.  
Here is a video about how the Shofar is made.

And here is an amazing service including the Shofar.

So to all my Jewish Friends I wish you a Happy New Year.

Ketiva VeChatima Tova