1. The Mishnah discusses the payment of a "Kolbon."
2. There is a dispute about the value of a Kolbon.
3. There is a dispute about whether Kusim are considered Nochrim or Jews.
4. The Gemara expounds on the Mishnah's comment that we accept Olah offerings from Nochrim.
5. Hashem took a fiery Machatzis ha'Shekel from under His Throne of Glory and showed it to Moshe.
A BIT MORE
1. A Kolbon is a small amount paid together with the Machatzis ha'Shekel. Some say that it is always given with every Machatzis ha'Shekel, while others say that it is given only when two people pay a full Shekel together.
2. Rebbi Meir: The value of a Kolbon is one Ma'ah (an additional 1/12 of a Machatzis ha'Shekel). Chachamim: It is a half-Ma'ah (an additional 1/24 of a Machatzis ha'Shekel).
3. Raban Shimon ben Gamliel says that Kusim are considered Jews, while Rebbi says that they have the status of Nochrim (see Yevamos 24a).
4. However, we do not accept their donations towards the building of the Beis ha'Mikdash or for building up Yerushalayim.
5. Hashem told Moshe, "Like this shall you give." This shows that one must give a Machatzis ha'Shekel that is pure silver. This is also a reason for why one must add a Kolbon -- it is given in order to make the half-Shekel equal to a Machatzis ha'Shekel of pure silver.