There are only operands and operators. Operands are also called mnemonics (pronouned new-MON-ix).
Binary is not a thing. It is a numbering system, like hex or decimal. It is not a what, but a HOW you look at RAM.
If I look at a location in RAM in decimal I might see 0. If I look at it in hex, it might see 0x00, and if I look at it in binary I might see 00000000.
All the same thing no matter how you look at it.
Thus, to create assembly, you simply, using specific rules about your processor, create a 32-bit number whose bits reflect those that tell the processor what mnemonic it is, and then what its operands are. You might have to create a couple of other 8, 16, or 32-bit numbers to go with it, depending on the processor syntax for the given mnemonic.
If you want to see what bit pattern an assembly instruction (again, a mnemonic, or operand) requires, you should get a processor book from the maker of that chip (eg. Motorola or Intel), or get a book at the bookstore about that chip.. eg. 8088, or 80386, etc.)
So to recount: Let's _suppose_ you had an LDA mnemonic for "Loading a value into an Address location". It might be assembler like this:
In binary, you have to know how the processor knows what a register is (and hence what index applies to what register). You have to know how many bits are used to tell the CPU which mnemonic it's looking at.
LDA #5,bx ;put a 5 into register bx
LDA #10,ax ;put a 10 into register ax
MUL bx,ax ;multiply the 2, putting result into bx
For example, Let's say all mnemonics require 6 bits to tell the CPU what the mnemonic is. You need 3 bits each for each registor (your imaginary processor only supports 7 registers), you need a sign bit, and a value for the operators.
LDA #5,bx might look like this:
Which, in decimal is: 3892314451, or
in hex is: 0x00E8000153.