Curriculum and instruction are intrinsically tied together in the field of academia. One can exist without the other; however, to allow such a state would certainly be detrimental to the teacher, student, and the entire educational system.
The curriculum is the plan laid out by the school for a particular grade, year, etc., while instruction is the way in which the teacher will execute those plans.
For example, the tenth grade reading list might consist of several novels such as The Natural and Catcher in the Rye. The school insists that all of the tenth grade students must read both of these books during the course of the year. Both of these works would then be considered to be part of the curriculum. It would then be up to the teacher to decide how he or she wants to read the works.
In some schools, however, the ways in which teachers must instruct is very specifically defined. In other schools, the teachers have more choice:
In any case, since the books are part of the curriculum, the teacher must convey the instruction on the books to the students in some form or another.
Essentially, through instruction, the teacher conveys the demands and requirements of the curriculum to the students.
Looking at how both of these aspects of education are developed will help to further your understanding of the relationship between them.
Curriculum is generally developed by a department at large, with input and requests from both the administrative units of the school, the requirements of the district, and mandatory proceedings from the state. In schools that do not receive state funding, these state requirements do not always have as much of a role.
Schools vary in their degrees of liberality towards the issue of the curriculum. Some institutions might allow teachers to develop their own personal curricula by using state standards and regulations, while other schools will have a set system that all of the teachers within a particular department have to follow.
Curricula will usually include a decent amount of information. However, you might find these snippets of similar or different wording within the context of a curriculum.
Schools differ in who is able to make up the instruction methods.
Schools which do not have a strict curriculum to follow will almost always be less strict with their requirements for how a teacher should instruct in the classroom.