If I have bruised ribs from a car wreck and they told me my platelet count is low and where my ribs are bruised is bleeding what can that be?

Low platelets... Low platelet count (thrombocytopenia) can cause bleeding. Platelets normally stop blood loss by clumping and aiding in blood clotting.
Bruise. When your platelet is significantly low and you have trauma -yes, you can have bleeding. Bleeding can happen in the skin tissue ( you see as a bruise) , or tissue underneath the skin or perhaps even on the deeper tissue- ( hematoma- accumulation of blood) depending on how significant is your trauma. Sometimes, bleeding can happen even without trauma if your platelet is very very low.