Before us is Mishnah 5 in the second chapter of Maseches Gittin. This Mishnah discusses who is qualified to write the get, and who is qualified to serve as an agent to bring it.
"Hakol kesheirin lichtov es ha-get" - all are qualified to write the get:
The Mishnah opens by establishing that all are qualified to write the get - "afilu cheiresh, shoteh v'katan" - even a cheiresh (a deaf-mute), a shoteh (one who is mentally incompetent) and a minor. The Gemara explains that the qualification of a cheiresh, shoteh and minor applies only to writing the tofes, the standard portion of the document of the get, and not to writing the toref, the details unique to this particular get, for which they are not qualified.
The Rishonim disagree as to whether their writing of the tofes requires a competent adult standing over them:
First opinion: Even for writing the tofes, a competent adult must stand over them and instruct them to write lishmah, for the sake of this particular husband and wife; whereas for the toref, even having an adult stand over them is of no help.
Second opinion: For writing the tofes there is no need for an adult standing over them, and if an adult did in fact stand over them, even the toref is valid after the fact.
"Ha'ishah kosseves es gitah v'ish kosev es shovaro" - a woman may write her own get and a man may write his own receipt:
A woman may write her own get, and afterward she hands it to her husband, who has the witnesses sign it and gives it to her for the purpose of divorce. However, if the parchment belongs to her, she must give it to her husband as a gift or in a manner that transfers ownership to him, since the materials of the get must be his. Even today, when the get is written by an expert scribe who brings all the materials with him, the scribe transfers ownership of the materials to the husband and tells him: "You are acquiring these materials, and I am merely acting on your behalf," for the husband must be the owner of the materials of the get.
So too, a man may write his own receipt. The shovar is a receipt, and it can be used in connection with payment of the kesubah: after the husband has paid the kesubah, the wife gives him a receipt. Normally a receipt is written by the one who gives it, but here the husband is the one who receives the receipt, and nevertheless he may write it, since the identity of the writer has no halachic significance. The wife, of course, will need to sign it if her signature is required.
"She'ein kiyum ha-get ela b'chosmav" - for the validation of the get depends only on those who sign it:
This is the reason a woman is qualified to write her own get - the validation of the get comes about only through those who sign it. According to the opinion that "eidei chasimah kartei," the signing witnesses are the ones who effect the divorce, the word "chosmav" is understood in its plain sense: the witnesses who sign the get, who are the primary witnesses. But even according to the opinion that "eidei mesirah kartei," that the primary witnesses are those who observe the handing over of the get, one can understand that the word "chosmav" refers to them, since the practice was to use those very same witnesses for both purposes.
"Hakol kesheirin l'havi es ha-get" - all are qualified to bring the get:
All are qualified to serve as an agent to bring the get, "chutz mi'cheiresh shoteh v'katan" - except for a cheiresh, a shoteh and a minor, and in addition to them - "v'suma v'nachri" - and one who is blind and a non-Jew:
A cheiresh, a shoteh and a minor: They are disqualified because they lack the mature and proper understanding required to serve as agents.
One who is blind: His disqualification has nothing to do with understanding. Rather, the reference is to a particular case in which the agent brings a get from overseas, from outside Eretz Yisrael, and he must declare "b'fanai nichtav u'v'fanai nechtam," it was written in my presence and signed in my presence - and a blind person cannot say this.
A non-Jew: He cannot serve as an agent to bring a get, and likewise not for kiddushin, since a person cannot serve as an agent for a matter to which he himself has no halachic connection and which he cannot perform himself. And since a non-Jew has no connection to gittin and kiddushin, he is not qualified for this agency.
In summary: In this Mishnah we learned that all are qualified to write the get, even a cheiresh, a shoteh and a minor - for writing the tofes but not the toref, and there is a dispute as to whether a competent adult must stand over them; that a woman may write her own get provided that the husband acquires the materials of the get, and that a man may write his own receipt, since the identity of the writer makes no difference; and the reason for all this - "she'ein kiyum ha-get ela b'chosmav." We also learned that all are qualified to bring the get, except for a cheiresh, a shoteh and a minor, who lack understanding, one who is blind, who cannot declare "b'fanai nichtav u'v'fanai nechtam," and a non-Jew, who has no connection to gittin and kiddushin.