Lot of people ping me some times for a sample usage session of radare to help to understand how the shell works and how to perform the most common tasks like disassembling, seeking, binary patching or debugging.
I hardly encourage you to read the rest of this book to help you understand better how everything works and enhace your skills, the learning curve of radare is usually a bit harder at the beggining, but after an hour of using it you will easily understand how most of the things work and how to get them cooperate together :)
For walking thru the binary file you will use three different kind of basic actions: seek, print and alterate.
To 'seek' there's an specific command abreviated as 's' than accepts an expression as argument that can be something like '10', '+0x25' or '[0x100+ptr_table]'. If you are working with block-based files you may prefer to set up the block size to 4K or the size required with the command 'b' and move forward or backward at seeks aligned to the block size using the '>' and '<' commands.
The 'print' command aliased as 'p', accepts a second letter to specify the print mode selected. The most common ones are 'px' for printing in hexadecimal, 'pd' for disassembling.
To 'write' open the file with 'radare -w'. This should be specified while opening the file, or just type 'eval file.write=true' in runtime to reopen the file in read-write-mode. You can use the 'w' command to write strings or 'wx' for hexpair strings:
> w hello world ; string > wx 90 90 90 90 ; hexpairs > wa jmp 0x8048140 ; assemble > wf inline.bin ; write contents of file
Appending a '?' to the command you will get the help message of it. (p? for example)
Enter the visual mode pressing 'V<enter>', and return to the prompt using the 'q' key.
In the visual mode you should use hjkl keys which are the default ones for scrolling (like left,down,up,right). So entering in cursor mode ('c') you will be able select bytes if using the shift together with HJKL.
In the visual mode you can insert (alterate bytes) pressing 'i' and then <tab> to switch between the hex or string column. Pressing 'q' in hex panel to return into the visual mode.