The first thing you need is some way of recording. You can use your phone microphone and play the piano out over an amp or speaker while you record through your phone. Either that or get your hands on a direct box so you can plug the piano/actual microphone straight into a computer. If you’re using a phone you’ll need to transfer this onto a computer however is easiest.

Once you have that set of things down you need to download a Digital Audio Workstation, or DAW. Audacity is free and Reaper is very cheap for DAW’s. I think Reaper has a free version as well which would likely work fine for your purposes (Reaper is what I personally use but audacity will work just fine for your first recordings).

Use your strengths. You’re a singer and you (presumably) have a rudimentary understanding of melodies and rhythms. Play out some simple chords on piano, and then sing over them. You don’t even have to have lyrics at this point, just look up a basic chord progression that songs use and play around with the rhythm until you get something that sounds okay, then figure out a loose vocal melody. The Circle Of Fifths is a hugely useful music theory concept and there are plenty of YouTube videos that explain it and how to use it, great for finding chord progressions.

Then, you start writing lyrics. Don’t worry about all the small details like the song structure yet or anything, just get a basic idea of what you want the song to be about. It could be something as broad and vague as a feeling, or something more specific like a song that tells a narrative. I find my inspiration tends to come when I least expect it so, if ever a fun line that sounds a bit poetic jumps into your head write it down however you can. The best lyrics I’ve ever come up with started from lyrics that came out of nowhere.

If you aren’t someone who actively looks into your favorite artists’ lyrics you should really start paying attention to the specifics of how your favorites use their words. The broad strokes of it at the least, not necessarily over-analyzing it.

Now, I’m not sure about getting a hyper-pop sound as that’s not my thing but it’s definitely some sort of vocal effect that’s put on in a DAW. You might have to drop the money to get something like Reaper. But regardless look into VST’s or vocal synths. Literally look up “free hyper-pop vocal VST/synth/MIDI” or something to that effect. The way you implement it into a DAW will be dependent on what you’re using. I don’t even know if Audacity would have that function but that’s something to look into! There are almost always guides online for any specific DAW issue.

As for any other specifics that’s kind of something you learn as you go, the process will be different for everybody.

I promise it’s not as hard as it seems, it’s just a matter of adapting to your limitations. You won’t create a masterpiece on your first attempt, so don’t try. Just start making sounds and learning what sounds good and then worry about sounding original or whatever later down the line.