What is the Torah referring to when it writes "u'Venei Yisrael Asu ka'asher Tzivah Hashem es Moshe"?
Rashi, Ramban #1 (both citing the Sifra) and Targum Yonasan: The Torah is referring to the Mitzvos concerning Sekilah mentioned elsewhere - pushing the culprit down from a high place, stoning him and hanging him 1 (and leaning their hands on him, 2 which was commanded in Pasuk 14 - Ramban, Moshav Zekenim and Targum Yonasan).
Ramban (citing the Ibn Ezra): It means that, from now on, Yisrael carried out the laws mentioned in the current Pesukim. 3
Ramban #2 and Moshav Zekenim #1: It means simply that Yisrael carried out the stoning just as Hashem had commanded Moshe. 4
Ramban #3, Seforno and Moshav Zekenim #2: To teach us that they stoned him (not out of hatred, but) in order to fulfill Hashem's command.
Ramban: Not leaving his corpse hanging on the tree after sunset.
Targum Yonasan also adds burying him.
See Ramban's objection to this explanation in Bo Shemos, 12:28 and Bamidbar, 1:54.
Ramban: As the Torah often does in connection with commands that Hashem commanded Moshe - See for example Bo Shemos, 12:28 and Bamidbar, 1:54.
What do we learn from the word "Oso"?
Refer to 24:14:151:1 and note.