The lesson objective is the main goal or purpose of the lesson. It's what you want your students do be able to do at the end of the lesson.
For example, when working on the topic of food, I may want students to write a recipe in English. In order to write a recipe, they need to understand ingredients and measurements in English. I would break this project into days.
Day 1: Students can name and identify the foods they commonly eat.
Day 2: Students can correctly measure using cups and ounces.
Day 3: Using a dish they make regularly, students can list the amounts of each ingredient they use.
Day 4: Students can write instructions for how to cool a dish they make regularly