The hard way: Download the processor manuals and code the opcode and operands by hand The easy way: Use an assembler program. The instructions are slightly different for each program, so try reading the manuals.
An opcode is a single instruction in assembly language. An operand is the data it does something with. For example, in "MOV r0, #0C", MOV is the opcode ("move this value into this register"), while...
Using " Has " is referred a past tense. Such as: He has taken the garbage out already. Using " Is " for example is referred a Present tense. Such as: He is taking out the garbage.