The best possible interface to use is SillyTavern. If you have a desktop OS available (macOS, Windows, Linux) and a little computer-savvy, it is strongly recommended to use this interface.
You will additionally need a backend, as well as some cards to use with SillyTavern.
Mobile hardware has become increasingly powerful. Recent hardware is more than capable of operating Character Cards. Several options exist for performing inference on-device or remotely. LocalTavern and ChatterUI provide integrated interfaces for inference on iOS and Android respectively. Android has several additional options for backends available, if somewhat complex to configure.
These can be utilized from any device and usually include a library of Character Cards for immediate usage.
People new to this pastime need several items:
The more of these can be provided in a single interface, the better a starting point it is for new users.