Hi,
There are at least 6 ways to do so, here are a few:
1. Point to the bar of task 4, keep the left mousekey down, draw a line to
the bar of task 22
2. Select a cell of task 4, now hold the ctrl hkey and select a cell of task
22; release the ctrl key and click the link tasks icon on the toolbar
3. In the predecessors column of task 22 type 4
4. Double-click on task 33 to show Task information, in the predecessors
path select 4.
Hope this helps,