The Mishna on today’s daf deals with two distinct issues.
1. If something that cannot be moved on Shabbat is connected with an object whose use is permitted on Shabbat, it can be used. The Mishna teaches:
A stone that is in a gourd used to draw water [kiruya], if they fill it with water and the stone does not fall, one may fill with it on Shabbat, and if not, and the stone does fall, one may not fill with it. With regard to a vine branch that is tied to a pitcher, one may fill water with it on Shabbat because the branch became part of the vessel.
Different vessels are fashioned from various kinds of gourds, especially from the species Lagenaria vulgaris. These vessels include jugs, buckets for drawing water, and dishes. Since these vessels are particularly lightweight and float on water, it is necessary to place a rock inside the gourd to draw water from a well or a stream.
2. It is forbidden to build a building on Shabbat, and even adding to an existing building on Shabbat is forbidden by the Sages. The Mishna teaches:
With regard to a window shutter, Rabbi Eliezer says: When it is tied to and hanging from the window, i.e., it is not touching the ground, one may shutter the window with it, because it is not considered building; and if not, i.e., it is touching the ground, one may not shutter the window with it. And the Rabbis say: Both in this case and in that case one may shutter with it.
In talmudic times, the window shutter was typically tied to and hanging from the window. At times, wood that was not attached to the window was placed in the window as a shutter. When not in use, it was placed alongside the window and utilized for other purposes as well.
There are various opinions among the commentaries with regard to a window shutter. Rashi holds that the prohibition of building temporary structures applies only to a roof and not to walls. Therefore, the window here is a skylight in the roof. That opinion was rejected in Tosafot. With regard to the shutter, some say that it is referring to a piece of wood that is neither connected to the window by a hinge nor by a rope (Me’iri). Other commentaries state that this is referring to a cloth curtain that slides open and closed (Rav Natan Av HaYeshiva; Rambam’s Commentary on the Mishna).