Got the first local cherries of the season at this morning's farmers market. Ben Clark of Clarkdale Fruit Farms told me that they would have sour cherries for probably two more weeks, and also about two weeks of sweet cherries, starting next week. You have to get there early - they sell out! Sour cherries (aka tart cherries or pie cherries) can be eaten fresh but really where they shine is in pie and preserves. So each year I try to get some into the freezer so we can have our cherry pie at Thanksgiving, plus a few other times if at all possible.
To freeze cherries, just wash, stem, and pit. Drain off an excess juice, then pack them into freezer bags (1 quart size is good).
An inexpensive cherry pitter is very helpful for the job. I picked one up a few years ago and have been grateful for it each year since. Pit cherries in a nice deep bowl, as they tend to spatter and the dark ones stain.
Plan on two quarts of fresh cherries yielding around 1 1/4 - 1 1/2 quarts of pitted cherries, well packed - just about the right amount for a pie.