없다 is a Korean verb which literally means to not exist, although this often is used to show the lack of possession (i.e., to not have something) though it technically doesn't take any direct objects-meaning you cannot quite use it like you would in English with the verb "to not have". In any case, you will also see it appear in various verbs based on speech register/level of politeness or humility. The three most common for survial purposes are:
없다 (dictionary form/very informal)
없어 (informal)
없어요 (formal, generic politeness)
You will likely use 없어요 for the vast majority of your communication in Korean.
Survival Korean
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Survival Korean