Once the PC is connected to the Android phone via a USB cable, you can access the SD card in your phone using the following steps.

 

Drag the notification area down by dragging it from the top of the screen where the date/time is shown.

 

And you will see the message USB connected.Tap on it.

 

And then you'll see a dialog, which allows you to select Mount, or Don't Mount.If you select Mount, then your SD card is now available to your PC as a drive.

If you select Don't Mount, then nothing happens, and if you want to mount it again, you have to disconnect and reconnect the Android to the PC.

Alternatively, you can activate the Task Manager at this point to switch to another task and defer the decision to a later time, when you can activate the Task Manager system again to switch to the Android task to see this dialog again.