Halakhah su Esodo 21:11

And [it] is only practiced at the time that the Jubilee is practiced (Gittin 65a). And one who transgresses it and does not designate her - not for him, and not for his son - and does not help with her redemption, has not performed this commandment. However it appears that we do not coerce him about the fulfillment of this commandment; as behold, it is written there explicitly (Exodus 21:11), "And if he does not do these three to her." [From here,] it is implied that the Torah left the thing up to his will. But if he married her as a wife or married her to his son, as we have written, he has done what his fitting. And a blessing will come upon him and good and proper children are fitting to come from their union.

That is that He commanded us to marry with kiddushin: To give something into the hand of the woman; through a contract; or through sexual intercourse. And that is the commandment of kiddushin. And the hint to this is, "When a man takes a wife, and marries (which can also mean, has intercourse with) her etc." (Deuteronomy 24:1) - indicating that he effectuates [the marriage] with intercourse; and His saying, "And she leaves [...] and becomes" (Deuteronomy 24:2) - since just like the leaving (divorce) is with a contract, so too is the becoming (marriage) with a contract. And likewise have we learned that [it is effectuated] with money, from His saying about a Hebrew maid-servant, "there is no money" (Exodus 21:11) - to this master, there is no money, but there is money to another master. And who is that? The father [of a bride]. But kiddushin from the Torah is nevertheless explained to be with intercourse, as is explained in [various] places in Ketubot, Kiddushin and Niddah. And the regulations of this commandment have already been completely explained in Tractate Kiddushin. But women are not obligated in this commandment. And in the explanation, they said (Kiddushin 9b), "Kiddushin with intercourse, which is from the Torah." (See Parashat Ki Tetzei; Mishneh Torah, Marriage.)

That is that He commanded us to redeem the Hebrew maidservant. And that is His, may He be blessed, saying, "he must let her be redeemed" (Exodus 21:8). This redemption has many details and conditions and there are many regulations for it - and they have been explained in Tractate Kiddushin. And the law of the Hebrew maidservant is completely explained there. And in the Mekhilta (Mekhilta d'Rabbi Yishmael 21:11:1) they said in explanation of, "And if these three he does not do to her" (Exodus 21:11), "Designate (marry) [her] yourself, to your son, or redeem her." (See Parashat Mishpatim; Mishneh Torah, Slaves 4.)

To marry a woman with a marriage contract and betrothal: That we were commanded to acquire a woman in one of three ways before the marriage. And the sages elucidated these ways (Kiddushin 2a) - that they are money (monetary value), a contract and sexual relations with her. And about this is it stated (Deuteronomy 22:13), "If a man takes a woman and has sexual relations with her," which is to say [that] if a man wants to take (marry) a woman for himself, he should acquire her first with sexual relations. And about that which the verse stated (Deuteronomy 24:2), "And she shall go out [...] and she shall be," the traditional understanding came [to explain] that [just] like the departure (divorce) of a woman is with a contract - as we will write in this Order (Sefer HaChinukh 579), with the help of God - so too is [her] being with him; meaning to say, the acquisition of a woman is with a contract. And they, may their memory be blessed, also learned (Kiddushin 4b) that she is acquired with monetary value, since it is written about an Israelite maidservant (Exodus 21:11), "and she shall go out, there is no silver (monetary value)" - and the understanding about it came [to explain] (Kiddushin 3b), "'There is no monetary value' for this master, but there is monetary value (when she goes) from another master. And who is he? Her father."