One does not shake the four species on Shabbat.
The Lulav, Haddasim and Aravot are Muktza on Shabbat.
The Etrog is not Muktza and one may smell it on Shabbat, after making the Bracha that one makes upon smelling any pleasant smelling fruit (that one isn't about to eat):
On the other days of Sukkoth one should not smell the Etrog.
One should not smell the Haddasim during the entire 7 days of Sukkoth.
An Etrog may be returned to its wrapping on Shabbat and Yom Tov, but may not be wrapped in a new wrapper, since the wrapper will absorb the aroma of the Etrog. One may not add aroma to materials on Shabbat and Yom Tov.
Source: Kitzur Shulchan Aruch 137:7
Thursday, 19 Elul 5775