Seafloor spreading occurs mainly at mid-ocean ridges, which are underwater mountain ranges formed by tectonic activity. These ridges act as a boundary between tectonic plates, specifically divergent boundaries, where two plates move away from each other.
As the plates separate, magma rises from the mantle to fill the gap, creating new oceanic crust. This process continuously adds material to the ocean floor and pushes older crust away from the ridge. The Mid-Atlantic Ridge is a prime example of a location where seafloor spreading is currently happening, along with other ridge systems found in the Pacific and Indian Oceans.
In summary, seafloor spreading primarily occurs at mid-ocean ridges, where tectonic plates diverge, allowing magma to create new oceanic crust.