db means 'define bytes'. It's a method of labeling a memory area and ititializing its contents. dup means to repeat the following definition the indicated number of times. db 13, 10 defines the ASCII values for a carriage return (CR) and a line feed (LF). This is a common line ending from the days of teletype machines. Some modern systems use line feed only (called a newline), some use a carriage return only, and some still use both. You can't possibly hope to mess around with assembly language without some documentation. Invest some time reading it.