What is the relationship between convection currents, seafloor spreading, and the formation of ocean basins?

There is a direct relationship between the convection current, spreading of the seafloor and ocean basin formation.

During the time of divergent plate motion, two plates move in the opposite direction due to the convection current generating in the mantle layer, which forces the plates to move in the opposite way. This results in the formation of cracks on the seafloor, and with progressive motion, the seafloor spreading takes place, thereby forms a narrow type of valley, erupting the magma along with water. This, over some millions of years, turns into an ocean basin.

Thus, they are directly related to one another and are some of the major processes of plate tectonics.

Seafloor spreading occurs at divergent plate boundaries. As tectonic plates slowly move away from each other, heat from the mantle's convection currents makes the crust more plastic and less dense. The less-dense material rises, often forming a mountain or elevated area of the seafloor.