As long as he has it, you are engaged to me with this peruta (small coin) that I’m handing you right now, under the condition that I’m going to give you 200 zuz (ancient coin) at a later time. We consider her to be engaged under the condition that he gives her those 200 zuz at some point in time. When he does give her those 200 zuz, we consider her halachically engaged. So, really, we backdate it to the moment that he gave her that original peruta.
If he tells her, “You’re engaged to me halachically under the condition that I give you 200 zuz within the next 30 days,” if he gave her the money within 30 days, she is mekudeshet, she’s engaged, but if not, she is not engaged. Engaged, likewise, is here also. It works retroactively. If he tells her, “You’re engaged to me under the condition that I have 200 zuz,” we say that she’s engaged as long as he brings two edim (witnesses) later on to show that he has those 200 zuz. Once he shows her that 200 zuz, they are engaged. If he does not bring those witnesses, then we say she’s safek mekudeshet. She’s married and not married, and we treat her like she may be married. Therefore, she’s not allowed to marry another person until she has a get (Jewish divorce document) from this first man.
Last case of the Mishnah: al menat she’areh lach matayim zuz. If he says to her, “We’re married under the condition that I show you 200 zuz,” we say, harei zu mekudeshet v’yareh lah. She is engaged, but he has to show her the 200 zuz of his own money that he has: v’im her’ah al hashulchan (And if he showed it on the table). But if he’s a money changer, someone who does that for a living, and he has other people’s money in his possession, and he shows her the 200 zuz that’s really the property of somebody else and they’re not his, eina mekudeshet, they’re not married. We’re making the assumption that she agreed to the kiddushin (betrothal) only if he shows her the money that’s actually his.