A VM virtualizes an entire computer. A container just isolates a process on the computer that's already running. That one difference explains everything else.
Both technologies let you run isolated, self-contained workloads on shared hardware, and both are described as "lightweight virtualization" in casual conversation — but they isolate at completely different layers of the stack. A virtual machine runs a full guest operating system, including its own kernel, on top of a hypervisor that emulates virtual hardware. A container shares the host machine's existing kernel and only isolates the process's view of the filesystem, network, and process table using kernel features like namespaces and cgroups. That difference in what gets duplicated — a whole OS versus just process boundaries — is why VMs take minutes to boot and containers take milliseconds.