Titanfall is available for free for a limited time on PC as part of EA's Origin Game Time promotion. Obviously you'll need to be an Origin member and have the client installed in order to play it. Those interested in playing Titanfall simply have to add the game to their Origin game library and download it.
The free play event for Respawn's online-focused, future-leaning first-person shooter will only last for 48 hours.
Those interested in purchasing the game after the free trial period ends can do so and continue their progress from the trial.