How to put my music into my iPhone?

Before, I used to just add music through "On My iPhone" but I got a new laptop and got the latest version of iTunes & now I can't add music through that way anymore either. Help? Haha

Added (1). I meant "On This iPhone" ***

Add songs into a playlist
connect your device
drag and drop the playlist

ps make sure your device is synced with your itunes
or it may not work. I had this problem before just synced my device

Hit ctrl s to bring up sidebar.

Enable manual management of music and video.

Then just drag the songs you want to the iPhone tab on sidebar.

I've always done it that way - since my first iPod nano (1st gen) through my daughter's iPhone 5, mom's iPad 3 and my son's iPod Touch 4. I never do what the other iPod owners do - reinvent the wheel using iCloudm syncing or playlists. I always do it my way and never get stuck with the problems that everybody else complains about - my songs won't copy to it, my playlists are all messed up, can't get new songs to it w/o erasing the ones already there, etc.