The PowerCLI prompt is also available under the Start button.
If not, something must have gone wrong during the installation.
The folder you are referring to is the folder where the CLI Tools are installed, not PowerCLI. That is in folder C:\Program Files\VMware\Infrastructure\vSphere PowerCLI.
When you start plain PowerShell, you can perform the Add-PSSnapin from that prompt.
Afaik there are no 'vifs' commands in PowerCLI. I suspect you are mixing PowerCLI and the CLI.
Perhaps you better raise your question in the vSphere Command-Line Interface community.