I want to purchase Argo Smart Routing, but I don't really understand the traffic in the billing.

I see that Argo Smart Routing’s billing is $0.1 per GB of traffic. Is the traffic here all the traffic generated by the user visiting my website? For example, if I have a video on my website and the video has 1G, then if 10 users visit the website and watch the video, 10G of traffic will be generated and $1 will be deducted. Am I understanding this correctly?

Welcome to the Cloudflare Community.

Hosting disproportionate quantities of non-HTML content, such as videos, violates section 2.8 of the Cloudflare ToS. You would need to use a service like Cloudflare Stream or R2 to host non-HTML content if you want to use it with the Cloudflare proxy. Alternately, you could serve that content from a subdomain that is configured as DNS-only, but it would forsake any benefits provided by Cloudflare.