If you are using the O365 Project 2016 C2R client, you have received a new feature to link tasks using a drop-down in the predecessor/successor column. This is especially helpful in larger schedules in which you don't want to scroll up and down just to find the id of the task.
Original message here: https://support.office.com/en-us/article/What-s-new-in-Project-2016-111bcaf9-bc27-4c15-80e6-85e72630...
