Hi @patricia_a_rano
Welcome to the Canvas Community!
Keep in mind that you do not typically teach courses from a sandbox. At most schools with a campus-wide Canvas installation, section shells and their enrollments are created automatically through an integration with the school's SIS system. The only exception would be if you were using an FFT (Free-for-Teachers) shell to both build in and teach in, and your co-instructor were doing the same.
If you are not using FFT, then if you and the co-instructor are both enrolled in the section shell (integration may only enroll the primary teacher), you could each independently copy the content from your sandboxes in to the teaching shell, then clean up any inconsistencies.
Either way this works, if you are splitting teach and grading, then both teachers and the students must be in the same Canvas shell.
Let me know if you two are using FFT, or a Canvas-hosted instance of Canvas, and we can then clarify in a bit more detail to help you get started.
Kelley