There's a first steps tutorial.You've already done a lot of them,but skipping down to the later numbers should give some explanation on Spybot.
http://www.safer-networking.org/supp...teps-tutorial/
This page has some explanation on what Users Account Control is:
http://www.7tutorials.com/uac-why-yo...er-turn-it-off
...
The system scan should be scheduled to run from time to time(once a month,I think it is.),but to operate Spybot in a useful way,you can run a System Scan to check for and remove threats more than that,as needed.