Business Central AL Development Coaching

I am a beginner-level Business Central AL developer seeking guidance on a small task.

I need help with:
- Creating a new field in this approval entry table
- Assigning a global variable as a field value to the table based on order number

I also need coaching on how to define a global variable.

I prefer step-by-step written instructions.

Ideal skills for this project include:
- Expertise in Business Central AL development
- Excellent teaching skills
- Ability to provide clear, detailed written instructions.