Can't speak firsthand about a Galaxy A3 with Android 6.0.1, because I have a Galaxy S7 that is running Android 8.0.0.
But in the dropdown resulting from swiping down at the top of the screen down toward the bottom there is an item in small font with an upward-pointing USB-looking icon to its left, named "Android system file transfer".
If I tap on that line it expands to a 2-line presentation that shows "File Transfer" on the first line and "Tap here for more options" on the second line.
If I then tap on the second line, a new large window appears titled "Use USB to" with five radio button options available: charge this phone, file transfer, photo transfer, system update, and MIDI.
The second one is checked by default, "file transfer". This is the new titling I suppose for the USB connection option that in older Android/Samsung implementations used to be shown as "MTP". And this is the setting which is required in order to make the phone visible to the PC and Windows Explorer (note that it will appear as a device in Explorer, with no drive letter assigned).
I believe the standard drivers required to "see" the Android phone from Win7 and Windows Explorer should be automatically installed once the device is connected properly via USB cable. In my Win7 the Samsung S7 phone shows up in Device Manager as follows:
with the driver titled "Samsung Android ADB Interface".
Although it's been a long time that I've been accessing first my S4 phone and now my S7 phone from my Win7 PC, I also have the
Samsung USB Driver in my library. It says it's only needed if you are developing on Windows and want the Samsung Android device to be available in your development environment. I don't recall if I actually ever installed this driver. But I do know that for some time now other new Win7/Win10 installations have automatically installed the required drivers to access my S7 making them available to Explorer.
I do remember that with older versions of Android when I connected the phone I'd have to swipe down from the top of the screen to get a USB connection window to appear, and then I would have to manually tap on the "MTP" radio button option in order to make the phone visible because it wasn't checked by default. I think this has been changed and improved in newer Android versions, such as my current 8.0.0.