The Talmud asks where the Melachah of Hotza’ah (carrying from one domain to another) is mentioned in the Torah. Why does the Talmud search for a verse for the Melachah of Hotza’ah? The Talmud earlier (49b) states that Hotza’ah was done in the Mishkan, and any Melachah that was done in the Mishkan is prohibited to do on Shabbat.
Tosfot (DH Hotza’ah) explains that Hotza’ah is a Melachah Geru’ah, a “weaker” Melachah. (This is because Hotza’ah does not change the object upon which it is done. Alternatively, it is because the domains of Shabbat are Halakhic and not physical entities. Therefore, a verse is necessary to teach that Hotza’ah indeed is prohibited on Shabbat.