The base load energy consumption of your building is the minimum amount of energy consumed when the building is not in use. This is generally things that cannot be shut down such as refrigerators, security lights etc and if not managed properly can add up to a not insignificant amount of energy usage.
To find the base load using Advisor you can log into the system and check what the usage was outside of office hours, generally it is best to choose a time early in the morning (eg 3am) as that ensures that everyone has gone home from the previous day and no one is in the office early. The usage at that time is the base load usage using the current shut down procedure that is in place, you can find the average over many days if you wish to get a more accurate representation of the base load usage.
You should then ensure that the shut down procedure is being fully followed by doing a walk around once everyone else has left the building over the course of a week or so. By checking what the usage is the the mornings after you have gone through the shutdown procedure you can then see if it is being followed correctly by comparing the base load of when you do the checks vs when you didn't do the checks, these figures should be the same or very close to each other.