Step 1. Implement a simple calculator

Step 2. Create a file format that encodes sequences of instructions and operands for your calculator

Step 3. Create an interpreter for that file format that runs your file. Add an accumulator and flags that represent overflow and such. And a instruction pointer.

Step 4: Add comments support to your file format (optional)

Step 5. Add support for logical operators, comparisons to your file format and interpreter

Step 6. Add support for labels and jumps to your file format and interpreter

Step 7. Add support for a stack, memory and related operators to your interpreter

In the end you should end up with something like

https://yjdoc2.github.io/8086-emulator-web/compile