The ten days starting with Rosh Hashanah and ending with Yom Kippur are commonly known as the Days of Awe (Yamim Noraim) or the Days of Repentance. This is a time for serious introspection, a time to consider the sins of the previous year and repent before Yom Kippur. Around here repentance can be quite time consuming.
One of the ongoing themes of the Days of Awe is the concept that G-d has "books" that he writes our names in, writing down who will live and who will die, who will have a good life and who will have a bad life, for the next year. These books are written on Rosh Hashanah, but our actions during the Days of Awe can alter G-d's decree. The actions that change the decree are teshuvah, tefilah and tzedakah," repentance, prayer, good deeds (usually, charity). These "books" are sealed on Yom Kippur. This concept of writing in books is the source of the common greeting during this time is "May you be inscribed and sealed for a good year."
Among the customs of this time, it is common to seek reconciliation with people you may have wronged during the course of the year. The Talmud maintains that Yom Kippur atones only for sins between man and G-d. To atone for sins against another person, you must first seek reconciliation with that person, righting the wrongs you committed against them if possible.
Another custom observed during this time is kapparot. Basically, you purchase a live fowl, and on the morning before Yom Kippur you waive it over your head reciting a prayer asking that the fowl be considered atonement for sins. The fowl is then slaughtered and given to the poor (or its value is given). Some Jews today simply use a bag of money instead of a fowl.
And that concludes this Sunday's service. Peace Be With You
Ed. note: This picture has nothing to do with Rosh Hashanah but everything to do with getting parties started!