Firstly it should be pointed out that there is some overlap between these two subdisciplines of linguistics, just as there is overlap between, say, syntax and morphology. But you're not far from the right track when you say:
"the difference is that phonology deals with language sounds and phonetics deals with human speech sounds..."
This is close, but it doesn't encapsulate the distinction memorably. I suggest the following approximation:
- Phonology: how sounds pattern within a given language (stated in terms of "phonemes")
- Phonetics: the characteristics of speech sounds (stated with descriptions of speech those sounds, sometimes referred to as "phones") themselves
Crucially, a phoneme consists of a set of phones, plus a set of rules describing how those phones are distributed within a particular language.
So, if we refer to a "voiced palatal affricate" [dʒ] without context, we are describing a "phone" -- a speech sound which is produced through a particular combination of articulations.
However, if we make a statement like "In Japanese, the phoneme /d/ has the allophone [dʒ] before the vowel /i/," then we are describing the patterning of phones in Japanese. Thus, this is a phonological description.
Note that how a particular phone patterns may be different in another language.
In English, for instance, "deep" [diːp] and "Jeep" [dʒiːp] are distinct terms, so while the phones in question here are comparable (roughly) to those in the Japanese case, the patterning is different.
However, and this is where it gets a bit messy, it's usually the case that there are purely phonetic (articulatory or auditory) influences that "motivate" particular phonological distributions. In fact the example from Japanese above is of a sort that's quite common cross-linguistically, so much so that it's been given its own name, "palatalization." So, phonology can often be "explained" in terms of phonetics.
Both of these subdisciplines have huge literatures and of course I'm grossly oversimplifying, but hopefully that is a useful start.