Picked one up today to replace my whooped S3.What are some "must have" apps?Any good free anti virus/security programs?

You don't need antivirus if you just use your head.  Seriously.  Go into your security and set up your full device encryption first.  Then download and set up device manager.  Pykl is a good radar app for weather.

Device manager? Do tell.

How much of a nerd are you?

Root plus xposed modules open up quite a bit of customizations. Just make sure you flash twrp recovery and back up first.

I'm not very into all this hi tech stuff too much like a lot of guy's on here to be honest.Just looking for some basic simple things I can do without messing anything up .

What do you use your phone for and what would you like to use your phone to do?

Email,sending pics,browsing the web,shopping,Facebook ect...Just basic things.Not running a business or anything with it.

Get Inbox, Chrome, and Device Manager if you don't already have them.  Google Keep is a great way to snyc notes (grocery lists, to do lists, etc) across devices.  Give Google Play Music a try and spend some time in the Play Store browsing by category so see if anything catches your eye.

ETA

Also give Hangouts a try to see if you like it better than the included Messenger app.

Get a wireless charging kit -- about $15 on Ebay.  No more fiddling with cables to charge your phone.  

Now that sounds like a plan

I like Circle Launcher (available at the Play Store).

It allows you to group several different apps into one button.  I put all of my stock market apps in one, news apps in another, etc.

Reduces clutter.

One thing I had on my old Galaxy that I can no longer find:  a simple carbon fiber or similar wallpaper.  The only ones I can find are active; prefer non-active for the battery savings.

2048 - Game
Airdroid - sync pics/videos/files to laptop
Battle of Zombies - Game
Breaking News - Vija Anand
Cerberus Anti-theft - GREAT APP - MUST HAVE OUT OF ALL OF THESE
Clash of Clans - Game - there are several Afrcom clans
DOT Placard Lookup - fun on trips
Endomondo - sports tracker
Evernote - Notes
eVolve SMS or Textra - SMS replacement app that works with Pushbullet to allow you to respond to texts from laptop
GoodReads - Books
Google Chrome to Phone - send links/pics to phone from desktop/laptop browser
gReader - RSS reader
Hide it Pro - hide pictures, SMS, files, videos with PIN
HBO Go
iHeart Radio
Lastpass - password management
Netflix
Nova Launcher - homescreen replacement
Pandora Radio
Plague - Game
Pocketcasts - podcasts
Pushbullet - notifications to your PC
Quickpic - gallery replacement
Raindar - radar app
Send to Kindle - send long web reading to your kindle
Text Plus - send text messages from another number without using your plan's message allowance
Torque Pro - get an OBD scanner from Amazon for $15 to diagnose car problems
Wallpaper Changer
Waze - better than Google Maps for navigation
WeatherBug

There are plenty here http://bit.ly/12i6oYq