Click/Khoisan languagues possibly oldest in world.

Keep in mind that race/culture are tenuously related to language.

It is unprovable whether the Khoisan population even spoke an ancestor language of present-day Khoisa (more commonly spelled: Xhosa). It may have been introduced by a conquering tribe or entered another way.

Clicks are just what they sound like: clicking noises. You can make them with your lips, like a kissing sound (bilabial click), with the side of your tongue like calling a horse (lateral click), with the tip of your tongue like scolding someone (tsk tsk, alveolar click), etc.

Clicks have a lot of high-frequency energy in them, allowing them to be heard above other sounds and at a longer distance than some other speech sounds (like a solo piccolo playing above an orchestra). Because of this, they may have been used early in the history of language to communicate danger, or other ideas over long distances. In present-day Xhosa, they are simply normal everyday consonants like b, d, and g.

"Click languages" is a misnomer. There are no languages, nor were there any likely to have existed, consisting entirely of clicks. A so-called "click language" simply has one or more clicks as a sound (consonant) in some words.

Xhosa is actually a Bantu languague!