Free trial begins 8/23/18 at 11:00 AM PDT and ends 8/27/18 at 11:59 PM PDT
Download and install the Blizzard Battle.net desktop app and launch it, find it at https://www.blizzard.com/en-us/
Create a free Blizzard account, or log in with an existing account.
Click the Overwatch icon on the left-hand side of the Blizzard desktop app.
Select your region from the menu, then click 'Install' to begin the process.
Once installed, click 'Play' to begin.
Here's how to take part in the free trial on PS4:
"Search" from the top menu.
In the search field, type in Overwatch.
Select 'Overwatch Free Weekend' from the search results, click 'Download'.
Once the download and installation process is complete, click 'Start' to begin.
Go to the Xbox One Store, then select 'Search'.
In the search field, type in 'Overwatch'.
Select 'Overwatch: Origins Edition' from the results and click 'Free Trial'.
Once the download and installation process is complete, click 'Launch'.
Overwatch is free to play this weekend only. If you like it, you may get the standard edition on PC for $20.
The Legendary Edition adds some skins and what not. Nothing I want, but see this deal thread on a possible cheaper way to get Legendary for less on Amazon: