It is customary for the Chazan (cantor) to keep the Shofar (ram's horn) covered and concealed until it is ready to be blown. Between the different blowings of the Shofar throughout the prayers, they keep it concealed in a koracha or under a cloth. The reason is that the Midrash (rabbinic interpretation) says that when Avraham Avinu was performing Akedat Yitzchak, he concealed his son and put him aside to protect him from the Ayin Hara (evil eye) and from Satan, who might try to stop Avraham from being able to perform this great mitzvah (commandment) for Hashem.
We learn a great lesson from here: the greater the stakes and the greater the mitzvah, the more opposing forces there are trying to get us not to do it. Therefore, we keep the Shofar concealed, we keep it under wraps, and when we are ready to blow the Shofar, we are able to be Me'arvev (to confuse) the Satan by taking it out and blowing it. Yet the Chazan should make sure that before making the Beracha (blessing), he holds the Shofar underneath, so that as soon as the Beracha is done, he can immediately pick it up and go ahead and blow it without any interruption between the Beracha and the mitzvah.