We use essere to talk about the qualities of nouns or to identify something/someone.
Esserci is used to indicate the presence of something/someone in a specific place.
Esserci: C'è una farmacia qui vicino. (There is a pharmacy nearby.)
Essere: La farmacia è aperta. (The pharmacy is open.)
To conjugate the verb "esserci" we add "ci" (c' before a vowel) between the personal pronoun and the verb.
io ci sono
tu ci sei
noi ci siamo
voi ci siete
loro ci sono
We only use the c'è and ci sono forms to talk about the presence of something or someone in a specific place. But others are sometimes used to talk about attending an event or availability.
Also use esserci to talk about abstract concepts.
We can sometimes use esserci + object (without a subject and without adding a specific location) to mean "here/there" depending on context:
C'è Mario? (Is Mario here/there?)
Ci sono i tuoi genitori? (Are you parents here/there?)