You should familiarise yourself with the apparatus and the functions of the six taps. Click on a tap to get a closer view or examine a schematic of the vacuum line here.
Refer to this diagram as you proceed through the experiment.
Note how Tap 4 (the 3-way tap) is utilised to supply a vacuum or a positive pressure of nitrogen to an attached vessel at either of the tubes on the Schlenck line. (Taps 5 & 6)
Firstly, you should attach a clean dry trap onto the cold finger to the left of Tap 3 using silicone vacuum grease.