Where in the heck is Wattz Consumer Electronics?
Fallout 4: how to access the Automatron DLC
Fallout 4's first DLC pack is a string of robotic adventures rejoicing in the name of Automatron.
To access the DLC, you'll obviously need to purchase it either standalone or as part of the Fallout 4 season pass, and then download and install it. (It won't download automatically for PS4 season pass holders, unfortunately, so you'll need to find the pack on the PlayStation Store and manually initiate the download.)
Once that's done, fire up Fallout 4 but don't immediately load your save; check the new "add-ons" section of the main menu. If Automatron is listed, you're good to go. If not, check that you're signed in on activated console, and restart your system.
Once you get in-game, you'll need to progress past the introductory section - leave Vault 111, in other words - or load up an existing save. In either case, the DLC mission will be added to the list of quests in your Pip-Boy. Note that the challenges presented by the Automatron DLC are designed for reasonably high-level players, so you may not want to go chasing this quest line as soon as you get out of the vault.
When you're ready to go, the first step is to listen to the appropriate distress signal, which you can hear anywhere in the Commonwealth; just open the radio section of your Pip-Boy, select the appropriate channel, and listen to the whole message through at least once. This should update your quest log.
Location of Wattz Consumer Electronics
The next step of the quest is to "locate the ambush", which can be a bit tricky - depending on where you are when you hear the radio signal, you might not get a map marker (I didn't).
The radio message said the attack took place near Wattz Consumer Electronics. if you've never visited or have forgotten this dungeon, it's north of the Institute and the ruins of CIT. The map below shows it's location; you can see the unique Diamond City marker towards the bottom of the screen, which makes a handy reference if you don't recognise any of this. Click to zoom.