WAV files are about ten times larger than an MP3 of the same recording. Ogg is open and royalty-free, which game engines and open-source tools favour. WAV is at home in recording, editing and mastering; OGG is the usual choice for royalty-free audio in games and on the web. OGG is lossy, so keep the WAV original if you may need full quality later.
The defaults suit most files. Under Options you can choose the bitrate and trim the start and end.
The conversion uses your browser's own video and audio codecs (WebCodecs), with hardware acceleration where the device has it; the file is read from disk as it goes and can be up to 2 GB. Where the browser lacks a codec, the page falls back to the compatibility engine. OGG is written at 160 kbps unless you choose another bitrate.