Econ: Balance of Payments sector, please, private, 621, net

rohitdoshi

Can anyone please explain to me why: (CFAI p. 621)

Y= C+ I + G + X -M

goes on to be

Y= C + S + T ?


and how does X-M (net exports) come to equal the sum of Government sector + Private sector?

How do net exports relate to gov and private??

An explanation would be highly appreciated