How to put iTunes music on iPhone?

I know how to get music into my iTunes library but how to I get it in "on this iPhone" when I plug my phone in? ITunes is so confusing anymore. Lol
So basically when I sync my phone, all of the music from "'on this iPhone" gets put into my phone. So how can I put my iTunes library into it?
Sorry if it's confusing!

Accessing work folder from home?

I'm wondering what I can use to access (view and modify) a folder on my desktop at work from either my HP Laptop, iPad, or preferably my iPhone.
The folder contains excel sheets and word documents (basically a generic main folder that contains a folder for each of my customers and has multiple excel sheets in each customers folder). This folder is constantly growing/ changing and when I'm out of the office (which is a lot) I need to be able to look at the customers excel sheets to relay information (it would also allow me to throw away ~10 lbs worth of print outs I have).
I need to be able to access it through some sort of internet connection, but whether that is a website or some sort of shared folder I'm not sure. It also needs to be something free, not some web service I need to buy or pay monthly for.

IPhone activation using someone else's SIM card?

I recently factory restored my iPhone 4 AT&T and it has no sim card so of course it needs to be activated, and I lost mine months ago, if I get my sister's sim card and put it in, then activate my phone, then put my sisters sim back in her phone will I be activated? Will her phone be affected?

Added (1). Zack, I'm not trying to get service I'm just trying to make it work, like an ipod touch.

What happens if I snap my SD card?

So I want to cancel my provider (Like T-Mobile or whatever) for my iphone 4s, ans I heard that If you snap the SD card your number and provider will be erased andyou won't be able to receive calls. Please tell me if this is true, If it isn't please tell me how I can cancel my provider without calling them (because it takes to long)

Song ringtones for my Iphone?

I do all of the process right, but when I try to add the AAC file to my 'tones' library I don't have one? So how do I fix that, I have a 4s with the update.

How is my iPhone 5s already out of space?

Ok so my iPhone 5s holds 12+GB of data. I just got the iPhone 3 WEEKS AGO. I downloaded one tv show episode but I deleted it after I watched. My MOST storage-filling app is instagram (200-250MB) and I only have 16 possible apps. NO music, NO videos, yet I'm over storage capacity every other hour? I don't understand. Someone please help.