Nutshell phonetics of ejectives
Ejectives are sounds which are made on a laryngeal (glottalic) egressive airstream mechanism. In order to pronounce these sounds, the vocal folds in the larynx are tight together and the larynx as a whole is pulled upwards by means of the action of the suprahyoid muscles. This sudden upward movement of the larynx creates higher pressure above the vocal folds and this causes a brief egressive airflow that serves as the energy for plosives and fricatives. Only the latter two sound categories can be realised electively. Ejectives are by definition voiceless.
Ejectives are transcribed phonetically by adding an apostrophe superscript to the relevant plosive or fricative symbol.
Ejectives are quite common in languages of the world: they occur in languages of the Caucasus, in East Asian and African languages, and in North, Central and South American languages. They are nowadays very common in English too as the allophonic realisation of plosives at the end of utterances.