When you hoover over a task in the timeline view with your mouse, you will be able to see round bubble icons.

If you click on one of these and drag it to another task you will create a link between. 

The default link type created is "Finish-to-start"

If you want to change the link type between tasks it can easily be done by opening one of the tasks by right clicking on it and to choose "open in new tab" in the context menu, then change the link on the task. See below: