"Студенти" is a more general term. It could refer to a group of male students, or just a group of students you don't know the gender of (mixed group, for example).

"Студентки" is a gender specific term, it refers to female students only.

Студентки іs female students Студенти іs male students

Студенти we can say about both sexs (males and females (in the case only about males)). Студентки, only about females. Plural of course