Translation:The mountain is beautiful.
I've heard 아름다와요 be applied to people too, like 그 사람은 아름다워요 (that person is beautiful).
From what I've read 예쁘다 is purely looks, but 아름답다 had a deeper meaning as in it's alluring, has elegance, evokes a particular feeling of beauty, or produces an emotion.
I'm sure a native speaker could explain this better.
Functionally they're the same, the difference is made by the word to which it's attached. 이/가 is a subject marker particle, and which version you use depends on whether or not the final syllable of the noun to which it is affixed has a batchim (final consonant). -이 is used with nouns that end in a consonant sound (ㄹㄱㅅㅈ, etc) while -가 is used with words that end in a vowel sound(ㅣㅓㅏㅗ, etc).
산 has a batchim, ㄴ, so when it's the subject it gets the 이 subject marker. 캐 does not have a batchim, so when it's the subject of a clause it gets the 가 subject marker.
The same applies for topic marker 은/는 and object marker 을/를: if the noun has a batchim you use the version without a starting consonant.