This Module introduces and guides the use of the CARBONOFF 4.0 toolkit—a digital, Excel-based instrument designed to help small and medium-sized enterprises (SMEs) calculate, understand, and reduce their carbon footprint in an accessible and user-friendly way. It acts then as a technical manual for VET learners, trainers, company professionals, and sustainability advisors who wish to adopt low-carbon practices in their professional environment. It provides step-by-step instructions for data input, guidance on interpreting the results generated by the tool, and explanations of the methodological assumptions used in the calculations.