Your sentence is almost perfect! To make it clear and grammatically correct, you can say:
- Original: A step-by-step instruction will help you draw!
- Corrected: A step-by-step instruction will help you draw.
or
A step-by-step guide will help you draw!
Explanation:
• "Instruction" is often used in plural as "instructions" when referring to more than one step.
• Using "guide" or "instructions" in plural sounds more natural.
• The exclamation mark is optional depending on how enthusiastic you want your sentence to sound.
So a better version for a 7-year-old might be:
Step-by-step instructions will help you draw!