The most basic difference lies in their view of human nature. For Hobbes, humans are eager of power and under the state of nature we tend to kill each other. For this reason, we need a social contract (in order to survive). For Locke, the state of nature is not as pessimistic as Hobbes. We can colaborate, but the problem is in property. Locke wrote something like when we have issues of who is the owner of what (specially under scarcity) we need the social contract protecting our work materialized as property.
I recommend you Hobbes' Leviathan and Locke's Second Treatise of Government. It is everything there and quite clearer than I have tried to explain it.