When you're done creating your course, you have 2 main ways to publish it to your learners:
Publish your entire course directly:
Visit your course
Go to "Overview"
Click on "Course Settings"
Choose section 3: Settings
Scroll down and enable "Publish course to enrolled students", and/or "Publish course to the Library"
Publish one lesson:
Visit your course
Go to "Lesson Plan"
Choose a unit plan
Click on "Publish" to publish this specific lesson
You can do the same to all the lessons you want to publish