Shabbos, Chapter 21, Mishnah 2. This mishnah deals with how to remove a muktzeh object resting on top of an object that may be handled, and with the ways one may make use of the utensil underneath without moving the muktzeh by hand.
"Ha'even shel al pi hechavis - mateh al tzidah v'hi nofeles":
A stone is resting on the mouth of a barrel of wine, and a person wants to reach the wine inside. The stone itself is muktzeh and may not be handled directly. The solution: he tilts the barrel onto its side and the stone falls off by itself. Its movement is thus brought about indirectly, by way of moving it from the side.
"Haysah bein hechavios":
If the wine barrel is standing among other barrels, he cannot simply tilt it where it stands, since the barrels are made of earthenware and the falling stone is likely to break them. In such a case the mishnah permits "magbihah umateh al tzidah v'hi nofeles" - he lifts the barrel and carries it to another place, and there he tilts it onto its side until the stone falls off.
"Ma'os she'al hakar - no'er es hakar v'hen nofelos":
A similar case: coins are lying on a cushion, and a person wants to use the cushion. He shakes the cushion or tilts it, and the coins fall off by themselves.
The Gemara's qualifications:
Needing the object itself or needing its place: The requirement to shake the cushion or tilt the barrel, wherever that is possible, applies only when the person needs the object itself - to get at the wine or to use the cushion. But if he needs the space they are occupying, shaking accomplishes nothing, since the stone or the coins will remain in the very place he needs. In that situation he may move the cushion or the barrel as they are to another place.
Forgetting versus placing deliberately: All of the above applies specifically where he forgot the stone on the mouth of the barrel or the coins on the cushion. But if he placed them there deliberately before Shabbos, so that they would be there on Shabbos, the cushion and the barrel become a base for a forbidden object, and they too become muktzeh and may not be handled.
Cleaning the cushion on Shabbos:
The mishnah continues with a further halachah concerning the cushion. If dirt has stuck to it, one may wipe it off with a rag, but one may not put water on it - putting water on something made of cloth is considered whitening and laundering on Shabbos.
However, if the cushion was made of leather, one may put water on it until the dirt is gone, since putting water on leather is not considered laundering it. To actually launder it, a full washing, is already a problem; but putting water only on the soiled spot is not considered laundering a garment on Shabbos.
In summary: In this mishnah we learned how to remove muktzeh resting on a utensil that may be handled - by tilting the barrel or shaking the cushion; when one may lift the entire utensil and carry it elsewhere; the Gemara's distinctions between one who needs the object and one who needs its place, and between one who forgot and one who placed the item there deliberately, making the utensil a base for a forbidden object; and finally the law of cleaning the cushion - wiping with a rag for a cloth cushion, and putting water on a leather one.