If you're trying machine code, this could be for you. It allows you to enter machine code instructions into any area of RAM and insert break points to prevent you from crashing and losing the lot! If you find a mistake, you then alter your code and try again.
Although both instructions and data must be entered in hexadecimal, MCTT has a conversion command, and will also allow you to page through memory to see what's there. Perhaps the most fascinating command to novices will allow you to see the values in the Z80A CPU registers, so you can see whether your code is producing the desired effect.
This, of course, is no good if you don't understand the nuts and bolts of the instruction set and registers. Fortunately, MCTT comes with a small, but useful manual, which explains hexadecimal, registers and many of the common Z80 instructions.
You won't rush out and write Manic Miner after using this but, used with OCP's Editor/Assembler, MCTT will help when you reach that standard.