Or perhaps he [Rav Chisda] is asking whether the law is like Rabbi Eliezer, who said in our Mishna (ahead on 52b) that someone he went outside the Shabbos boundary 2 hand-breadths [or less], can go back inside [the boundary].

Also it is precisely stated: that it is a case where there were not enough people [to form a complete enclosure extending all the way back to the Shabbos boundary]...

Because he said to him: Rav Nachman [said] to make for him [Rav Nechamia] a wall of people, and [then] he will "enter". Why would he need to add the word "enter" [if the wall already extended his path inside the boundary]? Rather, what it means to say is: he [Rav Chisda] should make an enclosure (until) 2 hand-breadths [of the boundary], and then he [Rav Nechemia] would walk in on his own [passing through a 2 hand-breadth space outside the boundary] with no enclosure.

It's wall fell -- of a Sukkah

And he should not stand up a bed frame: That he has in the Sukkah [to stand] in place of the gap [in the wall]. And even though it does not look like a [prohibited] act of building [on Yom Tov] -- because it appear as if he is [simply] intending to clear out space in the Sukkah -- even so, it is prohibited. And this presents a difficulty to [Rav Nachman's instruction] which allows making a wall of people on Shabbos.

In order that he can eat, drink and sleep: The main Mitzva of Sukkah is [performed through] these 3 things.

And he can stand up a bed frame: Therefore we see that it is permitted [to set up something to create a wall on Shabbos]. And the Gemara is going to investigate the contradiction between these two Baraitot.

And if [it is] not [attached and hanging on the building], one may not use it to shutter [the window], because it is similar [to the prohibited act of] building -- since he is increasing the enclosure of the room. And even though it is only temporary -- because he will go back and open it up again.

But has it not been stated - that even the Rabbis only permitted to add [to an existing structure], for example, by shuttering a window, which is merely adding. But the Baraisa permits to make a wall from scratch.

Rabbi Meir invalidates - it is explained in Tractate Sukkah -- lest the animal runs away [which is Rabbi Meir's reason for invalidating using an animal as a Sukkah wall].

Because he did not do anything - since [the wall] does not complete a Sukkah -- even though it is making a enclosure [Ohel] -- it is permitted. He [Rabbi Meir] is holding that we do make temporary enclosures [on Shabbat] -- since he is not completing a Sukkah it is only a temporary enclosure -- and is permitted.

Say that you hear from Rabbi Meir - that he invalidates

An animal - because [of the reason] lest it will run away

A person - who has the awareness to stand [in place], or utensils, which do not move from their place -- have you heard him teach that? And this Tanna [in the second Baraisa] is stating that a person and utensils [are allowed, even though they may also be valid Sukkah walls], saying: one makes his friend into a wall, and stands up the bed frame.