If you have 3,000 CDs, then you most definitely do not need Match, iCloud, Spotify, Apple Music, Amazon Music or a subscription to any music service.
Your nephew, like everyone else below the age of fifty (or so), will tell you to use Spotify, because he doesn't have a lifetime's collection of music already. Likewise, ignore Apple's suggestion, you don't need it. By the way, regarding the age stakes, we may be close in age.
Moving forward:
Re-reading your original post, I realise that you mentioned that you have installed the Microsoft Store version of iTunes. That's fine, it's still an Apple product, but updates to it are automatic (unlike the version directly from Apple), which means that the Help menu will not have the Check for Updates option.
Now, you need to add your existing music to the iTunes (programme) on your current computer. I will refer to:
- Files - a song is stored on your computer as a file. To "open" a file containing music, you need a suitable programme, such as iTunes. iTunes uses these files when you ask it to play a song, or copy that song to your phone
- Songs (or Music) - what you want to hear. When you ask iTunes to play a song, it uses the file for that song
- iTunes Library - your music, listed in your iTunes programme, that you have stored on your computer or external drive. Note, the music is not "in iTunes", it is wherever it was when you added it to your library. iTunes is a database, music manager (where you can edit information about the songs, as well as adding them to Playlists) and it is a player
- Playlists - don't be surprised if younger people tell you that your music "has to be in a Playlist". It doesn't! Once you copy the music to your phone, you use the phone's Music app to play that music. You can play it by artist, album, or even by the list of songs. Not to mention (well, I am mentioning it) - playing by genre or even by composer (if the composer information is present)
- Genre - in case you haven't come across the term before now, the genre is the style of the music. One of the ways in which the iPhone and iTunes can list your music is by genre. So you can choose to play only music listed as a specific genre (if you wish to that is)
To recap - getting your music into your iTunes Library;
Either:
- copy the files (that is, the songs' files) on to your computer, preferably into the Music/iTunes/ iTunes Media folder
- if your computer's drive is not large enough - and many on modern PCs are not, leave the files where they are but make sure that the external drive is on and ready to read before each occasion that you start iTunes
Next:
- use iTunes' top bar menu File/Add Folder to Library, navigate to and select the top folder containing your music files. That will add all the music in each folder inside the one you select
- with this next suggestion, be careful: you can of course, select individual folders, but be aware that if you select a folder containing files that you have already added, they will be added again, thus crating a duplicate entry for a song
- there is also the File/Add File to Library, which allows you to seek out and add individual files, should you need to
Adding music from CD:
- if you still have CDs to add to your library, and your computer has a CD drive, you can use iTunes to copy from the CD into your Library. If your computer does not have a built-in CD drive, you may want to purchase an external one, that connects to your computer by the USB port
Once you have your music in your iTunes library, it is time to add it to the phone. That requires setting options in iTunes, but for now, I think you should concentrate on getting your Library in order, otherwise, this post will become too long and unreadable. So another day..
Your use of the term G'day suggests that you might be in Australia. Well surprise, surprise, I'm not - and it's time for me to think about sleep. So if you respond, asking for more guidance, it may be 18 hours or so from now (i.e. 1400 hours GMT on Tuesday) before I can reply.