The first Star Wars trilogy (i.e., not the prequels) relied hugely on practical effects and miniatures: actors in monster masks rather than CGI beasts, for instance, and real-world ship models to achieve all of those fantastic space chases.
The second trilogy (i.e., the prequels) used a huge amount of CGI, and these days, that tends to be the way you put movies like this together.
J.J. Abrams took the middle road. He wasn't about to let the years of technological advancement since the first trilogy pass him by, and today's CGI toys are far more sophisticated than they were in 1999 when The Phantom Menace opened.
On the other hand, going whole-hog CGI would destroy some of the things that make the original Star Wars movies special, so the model shop got to fire back up and get to work.
The result is a mix of old and new that matches the movie's vibe perfectly. This is a movie about the old giving way to the new after all, for the characters and for the whole franchise.
The CGI pops up where it needs to: Maz, for example, is a motion-capture creation performed by Lupita Nyong'o, while the outer space scenes are largely done on a computer. But the locations are real, and while Maz may be CGI, many of the patrons in her bar are plain old actors with masks.
That helps give The Force Awakens its retro feel without losing the cutting edge that's always defined Star Wars, and it's another smart decision in a movie production that is full of them.