Step 1. Press win+g
Step 2. Find the widget labelled "performance."
Step 3. If you can't find it, simply select it from the bar at the top.
Step 4. Select "performance options" from the top of the widget.
Step 5. In this menu you can choose which types of metrics are tracked, what color the counter is, and it's transparency. If you're only looking for a FPS counter, uncheck everything but the last option.
Step 6. Close the options menu and hover your mouse over the widget. A small arrow will appear in the bottom right corner.
Step 7. Click this arrow to shrink the widget to a less intrusive size.
Step 8. Lastly, move the the widget to whichever corner of your screen you want, select the pin, and start / continue your game.