“One” is a number — we use it to answer the question of “how many”, or to emphasize that there is exactly one of something. We can translate it into Chinese as 一 + the relevant 量詞. “A(n)” is just the indefinite article — the rules of English grammar require a determiner whenever we use a singular countable noun. If the noun is indefinite, then the usual determiner is “a(n)”, but it has no particular meaning. We can usually omit “a(n)” when translating into Chinese, or possible use 一 + the relevant 量詞 pronounced softly (neutral tone 輕聲).

Well i will love to be a language exchange partner

a / an = 冠词 one = 代词