You cannot use the free version for commercial work. If you generate more than $1,000 per year in revenue using Fusion 360, or if you work for a company that uses it, you must purchase a paid subscription (currently $545/year or $70/month).
The Autodesk Fusion 360 installer is lightweight. It will download the full software in the background. Do not interrupt your internet connection. free autodesk fusion 360 download