Translation:The machine is small.
why μικρή and not μικρο?
Because μηχανή is a feminine noun, so the adjective used to describe it must take on a feminine form too.
A more detailed explanation can be found here
Hope that helps!
Nouns with suffix -η in nominative singular are feminine , so (η) μηχανή. Link: http://www.lexigram.gr/lex/newg/%CE%BC%CE%B7%CF%87%CE%B1%CE%BD%CE%AE#Hist2