TI-89 Titanium Calculator?

I got this thing at the beginning of my freshman year because i figured i would go all the way and have it through AP classes in High school. I have no clue how to use it still. Im in AP Geometry so im not using it as much as i would in Algebra but i end up using my phone instead. I can't even figure out how to change it so it goes from fractions to decimals. Lol i feel retarded.