They screen memory layout on the Apple II was a clever hardware hack but makes programming the machine more difficult. I think you'd be better off using a "trainer", like a KIM-1 simulator [0] to get your feet wet. (The KIM-1 was made by MOS Technologies, manufacturers of the 6502, as a demonstration and prototyping platform for the CPU.)

If you can do simple exercises on a machine like that and get comfortable with simple operations (loops, memory addressing modes) I think you'd have a better time grokking something more feature-filled.

[0] http://retro.hansotten.nl/6502-sbc/kim-1-manuals-and-softwar...