Needs : is a present tense singular verb.-- she /he needs
Need : is a present tense plural verb used also with I and you-- .you/they / I need.
In the given sentence, the subject is singular : 'an illiterate person'. So, it needs a singular verb--'needs'. The sentence is in the present tense. Complete sentence: On the other hand, an illiterate person needs help and guidance at every step.