Tones & Pitch

The discussion about tones in conlangs has prompted me to ask a few
questions on the subject... Hopefully I can get some of these things
cleared up.

My little-publicized conlang, Teslan, originally had a system of tones
almost identical to that of Swedish. Later I realized I didn't really
know what I was doing, so I got rid of it. However, the idea of tones
for Teslan really appeals to me, even if implementing them might
require modifications to phonology and grammar.

Anyway, I've heard about tonal languages, like Swedish and Chinese,
and "pitch accent" languages (like Japanese and Ancient Greek?). Can
somebody explain these two systems, and give some examples? How are
they alike and how are they different?

Also, do tones develop as sound changes (I've heard stories about the
Scandinavian languages), or are there examples of natlangs that have
always had tones? How does one represent tones in IPA or SAMPA?

That's a lot of questions, I guess, but I'd appreciate any and all
information anyone can give me on the subjects!

Thanks,
-jk
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