Answer:
New crust, sometimes islands/mountains
Step-by-step explanation:
Divergent boundaries are when two tectonic places are moving away from each other. In the current configuration of Earth, that happens in the ocean.
When plates move away from each other, they leave a gap. That gap is filled with lava that solidifies quickly and forms now crust. If the ocean floor is relatively shallow, and the lava pressure is big enough, that can lead to the formation of new islands, mountains/volcanoes on top of the gap. That's basically how the Galapagos islands were created.