You can be notified of updates in a number of different channels.
For most people, you should leave this set to Stable. The update check results will then relate to stable, production releases of FoCal which will be good for everyone.
If you want to try some "nearly ready" featues of FoCal, you can choose the Beta channel. These versions will be generally feature complete, and will have had some testing but are not quite ready for a production release.
The Alpha channel is for those of you that want to try the bleeding edge releases. These will contain new and exciting features but they may not work correctly, and they may be removed from later development.
Further details are available on the FAQ page.
Please note: We very much welcome feedback on Alpha and Beta versions but we do not provide any guaranteed level of support for Alpha and Beta versions of FoCal.