To access myCloud via WebDav, you need a WebDav-enabled client. This is software on your computer or smartphone that provides access. Windows as well as macOS have an own client by default. Here you can find the instructions on how to use the Windows Client as well as the macOS Client.
How fast and stable WebDav works depends very much on the client used.
If you have issues with stability and/or speed we recommend the use of specialized software. There are many free and paid offers on the Internet.