The command file is plain text. You can double-click it and it'll open in Notepad, like any other text file.
Let's take a moment to dissect the sucker.
#GAME NAME: Final Fantasy 1 (NES)
#BLOCK NAME: Dialogue Block (RAW)
#SCRIPT START: $28210
#SCRIPT STOP: $2B496
#COMMENTS: Yes //start first line with //
#END BLOCK //remainder of comment placement
//is handled by control codes
#BLOCK NAME: Dialogue Block (POINTER_RELATIVE)
#POINTER ENDIAN: LITTLE
#POINTER TABLE START: $28010
#POINTER TABLE STOP: $28210
#POINTER SIZE: $02
#POINTER SPACE: $00
#ATLAS PTRS: Yes
#BASE POINTER: $20010 //add $20010 to each pointer to get
#TABLE: ff1_ptr.tbl //the string address
The readme explains each command in more detail, but since you're having a little trouble grasping the basics here, lemme explain what you're looking at here.
Each block defined in a command file determines what gets dumped and how. If you look closely, you'll see these two blocks are actually the same block. That is, both will dump the same text, but using two slightly different methods.
"RAW" (dumped to ff1_script_000.txt, also a plain text file) is just the script, helpfully commented out. This might be your only option for more complicated scripts, but it's less than ideal, since it means you'll have to do all the formatting needed to insert it using Atlas manually. It starts dumping at the given start address and keeps going until it reaches the end address.
"POINTER_RELATIVE" (dumped to ff1_script_001.txt) is more Atlas-friendly. Instead of pointing Cartographer to the script, you point it to the pointer table, and it uses that to figure out where the strings are. As a result, the script dump will include the pointer writes Atlas needs to insert the script: you still need to add the header information so Atlas knows which table to insert with and whatnot, but the hardest part (the pointers) has been taken care of already.
Note that the two blocks take slightly different tables. And by "slightly," I mean that "ff1_raw.tbl" and "ff1_ptr.tbl" (also plain text files) differ by only a single line. The "/" before the "00" token in ff1_ptr.tbl is important: it denotes that this byte indicates the end of a string, and without it, Cartographer will simply dump the entire rest of the ROM over and over again until it's read through the entire pointer table. So be warned.
I don't know what makes you think tables have checksums, but the aforementioned sample tables will tell you what yours should look like. If you're completely lost, a table is a file indicating which byte values correspond to which characters. Again, in Cartographer's case, your table has to have an end tag defined if you're going to use the Atlas-friendly POINTER_RELATIVE mode, or Bad Things will happen (really, your computer will slow to a crawl for a short while and you'll have a huge whopping text file on your hard drive filled with redundant data).