Sorry for me sounding daft, I assume you mean to leave it on without using it and letting it run down. DoI need to turn off Wi-Fi or any other applications.
Don't be silly
No matter how much people may know now - they all started as beginners once
By all means leave everything on and use the heck out of it which will speed-up the battery drainage but you don't have to.
Just let it run right down (however you go about it) until it goes off and recharge it.
After 3 or 4 times of doing this, your battery will have calibrated itself properly and you'll get the 9 or so hours that's advertised
If you're going to get all of your apps from the Play Store (as and Android newbie - I'm guessing that's the case?) then you really don't need an anti-virus app.
Some do offer additional security aspects though such as locking and wiping in case of theft - Avast
is a good one.