Firstly, there’s some tools that you’ll need beforehand such as a SD card on your phone and a USB cable for uploading your files. So, of course, have your songs ready in another folder.
Hook up your USB Cable (Type B) to your laptop.
Go to Y2 Mate or any other Youtube MP3 Converter
One song I’ll be downloading for example is Kehlani – Hate The Club ft. Masego
Save to desired folder
Locate your music folder in Internal Storage
(locating my music folder -> Internal Storage from mobile device)
Next, pull up your MP3 that you downloaded or any other music you may have stored on your PC
Here’s a list of songs I like/have stored on my PC. I’ll apply the copy+paste method since I want to keep most of the songs on my laptop
Once you’ve copy and pasted all your favorite songs in the music fold (inside you internal storage/SD Card). You can now go to your mobile device and upload in Google Play Music
Here are a few screenshots from my mobile device