what is the difference between 'esse' and 'esst'?
They are different conjugations of the same verb.
essen (to eat):
ich esse (I eat)
du isst (you[sing. inf.] eat)
er/sie/es isst (he/she/it eats)
wir essen (we eat)
ihr esst (you[pl. inf.] eat)
sie essen (you[pl. form.]/you[sing. form.]/they eat)
sing. = singular, pl. = plural, inf. = informal, form. = formal.