Google Maps gives you the ability to use your current location as a start or end point when generating directions. To use this feature, click Get directions in the left panel. In point A start typing "my location" and you'll see My Location appear in the suggested items. Click the line item to populate the starting point.
In order to use My Location, you'll need to give Google Maps access to your physical location. In most cases your browser will pop up a notification asking if you want to give this permission. Otherwise you should see a warning pointing to instructions on how to fix the permission error.
Once you give permission, the dot next to My Location will turn blue, indicating the feature is enabled.