Generally speaking, иметь in this sense is a formal word which means 'possess, have as possession'.

I have a book. - У меня есть книга. - that's the normal way of saying. If you say Я имею книгу - that sounds quite formal, like 'I have a book in my possession'.

Иметь is often used in statistical or historical texts to express the idea of 'possession', e.g. Средний крестьянин имел дом и корову - An average peasant would have a house and a cow.