就 is often translated as simply "just", but there are some nuances to how it is used in Chinese grammar.
Structure with 就 meaning "only have"
就 can mean "only, or only have". When using it you can add 只 and 只有, or you can leave it out.
我 就 认识 一 个 中国 人。
Structure with 就 meaning "just one"
就 can also be used to express one person or thing, similar to how we say in English "just one person" or "just one left". It is often paired with 一个 or something like that.
就+single things or persons
这 件 事 就 我 一 个 人 知道。