Question

Is this right: If a subject is singular, then the verb have to be a plural.

Answer 1

You are looking for Subjects/Verbs Agreement:
http://owl.english.purdue.edu/owl/resource/599/01/
http://www.lincoln.edu/mhs/owl/svagreement.html

Answer 2

When you use third person singular, then you should add an 's' in the end of the verb. It is not 'plural' though. For example: 'I like to learn English.' but 'Joe likes to learn English.'