Can you download music to your iPhone from someone els iTunes?

I don't even know what to do in my iPhone settings to connect it to a computer someone please help

If the other person created the music and have made it available then you can. If someone else owns the copyright and distribution rights then other people have no right to share the music and you would be stealing it.

From your iPhones settings select…

Wi-Fi and tap the On button. Enter the password (if any) for the network you want to join.

Open iTunes on your computer. The iPhone will be listed under Devices. Drag the music you want from the iTunes library on to the iPhone icon and it will copy the music to the phone.

The problem with iTunes is that in order to block you from sharing, you realluy need a separate itunes installation for each phone. In fact even having several devices like an Ipad and Iphone is very difficult even though they say it is not if you are using a PC instead of MAC.
You need a unique itunes installation in a computer and it will have to have internet access running for installation. You will need to set up an account or user on itunes. You will need the iphone to USB cable that you received with your phone.

Apple wants to make money off of you for everything you do even if it is free to PC users. They are not interested in cinvenience or they would have dumped Itunes years ago.

You should look at clouds if you wanr to share not itunes. Better yet. Don't use Apple products.

@Duncan - He wants to connect to someone else's computer not his own.