If you've been waiting for an opportunity to take Overwatch for a spin to see if it's your thing, you should probably mark November 18 on your calendar. Beginning then and running until November 21, Blizzard is making the game free to play for everyone.
The free-play period will give players access to all 22 Overwatch heroes, 13 maps, and the Quick Play, Vs. AI, Custom Game, and Weekly Brawl game modes. Loot Boxes, leveling, and unlocks will all work as they normally do during the free weekend, and players who opt to purchase the game once it's over will retain any rewards and progress they've earned, as long as they do so using the same Battle.net account.
The free weekend will start at precisely (or at least, reasonably near to)11 am PT/2 pm ET on November 18. To get in on the action, you'll need to download the Battle.net client, and then Overwatch itself, which clocks in at a not-insubstantial 12GB—you might want to give yourself a little lead-time on that. Full details (although there's really not much more to it—Overwatch is free for a few days, so grab it and have fun!) are up at playoverwatch.com.