Once you've got your library started there are some basic things you need to do.
Edit Song Information
Your MP3 player will display information about the song as it's playing such as artist, album, and title. Edit the song's tags so that the information is correct. This also helps your music manager to properly sort the music in the library. Sometimes, the information is inconsistent (eg, Pink vs P!nk) so it's useful to standardize the tags in your library.
Create Playlists
So far, I haven't created any playlists because I just put my music on shuffle. Shuffle plays your music in random order, otherwise the player will always start in the beginning and play them sequentially, one after another.
Playlists are groups of songs. The music manager has default groups like Recently Added and Recently Played. You create any playlist you like and I may getting around to creating a Driving Songs playlist for road trips.
Re-Scan Folders
If you add, delete, or move music in your library via methods other than your music manager, you need to get your music manage to rescan the folders to make sure your library is kept current. iTunes doesn't have an explicit rescan function so you need to regularly "Add Folder to Library" using your existing music folders to get it to rescan your folders.
In MusicBee, new additions from rescanning my music folders are first placed in the inbox. This allows me to easily find the new music so I can edit the metadata tags. Once the edits are complete, I send new audio to its appropriate category (ie, music, audiobooks, podcasts).
Sync Music
Once your music library is ready to be uploaded to your portable/mobile device (ie, phone, USB stick, etc), you need a USB cable to connect the phone to your computer. Once connected, the music manager will recognize that there is a portable device plugged into your computer. Select the Synchronize (Sync) Portable Device command and the music manager will transfer your music over to your device.
Play Audio
Android comes equipped with the "Play Music" app. This works well enough but there are lots of other music players available from the Google Play store. I also like listening to podcasts and audio books and some apps work better than others for these audio files. Try a few out and pick the one(s) that work best for you.