An explanation of some of what you typed in to Xterm:

• grep searches for a word within a file (or other input); *nix people will often refer to needle (the word) and haystack (the file or other input)
• lock_code is the needle
• /dev/mtd1 is the haystack: the file which contains the hash of your lock code
• -A 13 tells grep to also show the 13 lines after the matching line in /dev/mtd1; this is because the hash is a number of lines after the occurrence of the word lock_code (guess how many?)
• | (aka 'pipe') means take the output of the previous command (the grep) and send it into the following command as input
• tail -1 means show only the last line of the input (the input in this case being the output of grep which you piped into tail)