Nice question. I can't exactly remember what the sounds were, but probably this would be getting hold of one of those mini cassette type dictaphone (I was a child of the 80's). This sort of thing:
The first real manipulation I remember started with my second computer, an Amiga A600. I remember my parents insisting on me owning a computer instead of a games console, largely with the idea that these were more 'productive' and 'educational'. I actually think they might have been right - I possibly would not be where I am today if it wasn't for that machine. So the fist manipulation of sounds goes to my A600 and OCTAMED:
It was incredible fun, I'd not record sounds in, but find them from other games and sequence them into awful sounding lofi nonsense...
I think it set me in good stead though. I later migrated to the amazing Buzz Tracker where I really started to learn some interesting stuff:
Then I moved sideways into sound design.. ah good memories indeed.