On screen keyboard / save input

Hello guys, noob here in need of some help. I am trying to make an on screen keyboard where i can use numbers and letters, i would also like to save the input. I have seen some codes online or YouTube videos but haven’t been able to get it to work.

I am currently using a 7" touchscreen display with an RA8875 driver and a arduino mega.

Any help is much appreciated, thankyou in advance