Static vs dynamic QR codes
Both scan the same way. The difference is what is stored in the pattern, and that decides whether you can edit it, track it, and whether it depends on a service.
Static QR codes
A static code stores the content itself: a link, a Wi-Fi name and password, a contact card or plain text. It works without any website, never expires and costs nothing. The downside is that it can never change, and nobody can count its scans, because scanning it never touches a server.
Long content makes a dense pattern with many small squares, which is harder to scan when printed small.
Dynamic QR codes
A dynamic code stores a short link. Each scan goes through the QR service, which records it and forwards the visitor to your current destination. That gives you editing after printing, scan statistics, scheduling, passwords, scan limits and rules that send different visitors to different pages.
Because the short link is short, the pattern stays simple and scans easily, even when the final page has a long address. The trade-off is that the code depends on the service staying up and your account staying active.
Which one to use
Use dynamic for anything printed in quantity or kept for a long time: menus, packaging, posters, flyers, business cards and signs. Use static when the content will never change and must work offline, such as a Wi-Fi code for your own router, or for a quick one-off code on a slide.
Before choosing a service for dynamic codes, check what happens when you stop paying. Here codes keep redirecting forever; codes beyond the free three only become read-only.