Creative consultant only
George Lucas sold his LucasArts production company — including the entire Star Wars franchise — to Disney Entertainment in 2012. This was prior to any production on The Force Awakens. In fact, it was this move that led to planning for a new trilogy.
George Lucas remains a "creative consultant" on all Disney-era Star Wars film projects, but this is a fairly amorphous role. For instance, he submitted rough story ideas for new Star Wars episodes to Disney. These were summarily rejected by the new film's director, J.J. Abrams, and producer Kathleen Kennedy. In the end, Michael Arndt, Lawrence Kasdan, and J.J. Abrams conceived the story for The Force Awakens without any input from Lucas.
Apparently, George was "happy not to be involved". Early in 2015, he said:
"I haven’t seen anything; I mean I saw the trailer, it looks great, it looks interesting. But as I’ve said before: one thing I regret about Star Wars is that I never got to see it, you know? I never got to be blown away by the big ship coming over the thing, or anything. But this time I’m going to be, because I have no idea what they’re doing."
All in all, he really had no measurable role in the film — apart from the fact that The Force Awakens is really uncomfortably close in plot to his original 1977 Star Wars film. In that sense, he contributed a lot to The Force Awakens.