The sequence is fairly easy:
Master Arm - ON
For fuel tanks (bombs and A2G missiles too), rotate the selective jettison knob clockwise to STORES
Select the appropriate stations using the buttons to the left of the IFEI engine display. (I have a feeling you are missing this step).
Push and hold the red JETT button until the selected stores have released.
Rotate the selective jettison knob back to SAFE.
De-select the stations you previously selected.
Master Arm - OFF
Hang in there! Getting started with a new aircraft is always a challenge, and all of us have been there before.
Diesel_Thunder's post in FA-18 Can't Jettison Drop Tanks was marked as the answer