There is no distinction between ‘he’ ‘she’ and ‘it’ in Turkish. The context gives the clue to the gender of the person involved.
Sen is the singular informal ‘you ‘rather like the French tu or the German du. Sen is used when speaking to close friends , family and children. Siz is used for acquaintances , people with whm you have only a formal relationship. In rural areas, however, this distinction breaks down and sen is used for anyone. If you are worried about giving offence keep to siz, but do not be put out if you are addressed as sen.
As the personal suffixes give the peson and number of subject, personal pronouns are generally not used as the subject of a sentence in colloquial speech.They are used to put special emphasis on the person, or to make comparisons or contrasts between people.