Classic Gmail (previous version) had a drop-down menu at the top left under Gmail to quickly access contacts. Now this drop-down option has passed the new interface.
In the new interface, you can see a square box in the upper right near the bell icon. This has several Google applications:
Click on this square box, the contacts will be there, if it is not there, click on Plus, you will find the Contacts:
You can rearrange these products at any time by dragging them.