My very first tabletop army

So I was a die hard Fantasy fan. Love the total war games (I main chaos undivided in case your curious) fan and then I found the necrons and it was really love at first sight.I guess I will be starting my very first table top army. So...I have no idea what the hell I am doing what the hell even is a "save" so wish me luck! Any advice is greatly appreciated for an extreme noob like me.