For questions concerning the International Phonetic Alphabet and its usage in Chinese phonology
The International Phonetic Alphabet is a widely recognized notation system to standardize the representation of sounds in any spoken language.
IPA is based on the latin alphabet, with additional symbols and diacritic marks. A sequence of sounds is represented between forward slashes. So for example the standard pronunciation of the English word "cat" can be written in IPA as
A description of Chinese sounds using IPA notation can be found on Wikipedia as well: Standard Chinese Phonology.
If your question is about notation systems or symbols that do not pertain to IPA, please use the tag [notations] instead.