CHARGEN brief documentation:
CHARGEN is a small assembly language routine that interfaces with BASIC so that you can use it in your BASIC programs. It runs on a PMODE 4,1 screen and is currently set up for a disk system (There are some POKE's that can be done to make it work with cassette; see the Galactic Revolution program loader REVOLT.BAS to see what to change). It supports true upper & lowercase with a pre-bolded font to make it easy to read even on a TV. It also gives you 32x24 text, letting you fit up to 768 characters on the screen at once versus the normal BASIC 512. It also features a few special CHR$ commands that you can PRINT:
    CHR$(8)  - Backspace
    CHR$(12) - clear screen and home cursor
    CHR$(13) - Carriage return
    CHR$(14) - Turn cursor on
    CHR$(15) - Turn cursor off
    CHR$(16) - Turn inverse on
    CHR$(17) - Turn inverse off
There are also special features that are controlled bye POKE's to certain memory locations:
POKE &HDC,(0-31): Set cursor X position
POKE &HDD,(0-23): Set cursor Y position
POKE &H200,(0-30): Set "window" area left position
POKE &H201,(0-22): Set "window" area top position
POKE &H202,(1-32): Set "window" area X size
POKE &H203,(1-24): Set "window" area Y size
By setting the values at &H200 to &H203 you can set up a special "window area" that text will scroll within (good for things like adventure games).

To use it currently requires a 32K RAM or higher Coco 1,2,3. You will need to do the following to load it:
CLEAR 200,&H79A8
LOADM "CHARGEN"
EXEC
After that, you can write you BASIC program, and mix PMODE 4 graphics commands with text.

NOTE: Only characters from 32 to 127 are defined (CHR$). Any values above that will print out some garbage (maybe you can use them for exploded items or something).