1only have ...; there is only ...
2(used in combination with 才) it is only if ... (that one can ...) (as in 只有通過治療才能痊愈|只有通过治疗才能痊愈 "the only way to cure it is with therapy")
3it is only (someone) who ... (as in 只有男性才有此需要 "only men would have such a requirement")
4(used to express lack of alternatives) can only; have no choice but to (as in 只有屈服 "the only thing you can do is give in")
Examples
xué学zhōng wén中文de的xué sheng学生zhǐ yǒu只有tā men他们jǐ几gè个。
学中文的学生只有他们几个。
They are the only students who study Chinese.
只有一点点的知识是危险的事。
A little knowledge is a dangerous thing.
只有几个学生懂那个方面。
Only some students understand that aspect.