Got it there as well.
View attachment 164538
Crystaltile2 is a fairly heavily featured program aimed at doing it all for GBA and DS games really. This would increase the complexity somewhat but just the same as you can use a word processor without having a clue how to add macros to your mail merge you can still do stuff here.
The link from my signature
https://gbatemp.net/threads/gbatemp-rom-hacking-documentation-project-new-2016-edition-out.73394/
It covers some usage of it.
Tiled2002 is a bit simpler as it just a tile editor.
In both cases it involves opening the ROM in the program (file -> open or some normal looking icon for opening things), selecting the mode (GBA 4bpp and GBA 8bpp being the best choices to start with on both counts). Then pressing down on the slider, or possibly page down a lot to see what you can see. It likely won't be the right colours (recall the palettes conversation from the previous post). For crystaltile2 then you will probably have to select the tile editor mode but it should be obvious there (if the screen is filled with squares then you have it, if it is a small square of squares then you are in edit mode and need the other one).
Similar deal for the compressed stuff -- open, let is scan, press next section a lot until you find something.
Similarly if it appears on screen like that then it might be worth having a look at the more in depth things like tracing (
https://www.romhacking.net/documents/361/ ). Both in the menu options, and in the final boss to see where the final boss sprites are kept and scanning around either side from there.