The comment above is great advice overall, but I break with it on the last paragraph. I think most people in the "I don't know C or electronics, but want to get into electronics and firmware" camp should start with Arduino (or clones).

Not because it's great technically and not because the editor is great (frankly, it's awful). The reason I argue to start there is that they've made the first 15 minute experience stupidly easy and convenient and, as a result, it's become wildly common and popular and you can readily find Arduino-platformed examples for most of the basic electronics technologies. If you're the type to learn best when you can see glimmers of visible progress, Arduino gives you smooth on-ramp.

You will need to wean yourself from that reliance/training wheels at some point, but I think it makes the first 2 months 20x easier, especially if you're trying to learn datatypes, bit-packing, pointers, memory management, analog electronics, digital electronics, communications protocols, in-circuit programming, and everything else (PCB design?) all at once. Break it up a little.