Current accounts as savings? The book I'm reading shows that
$$ S= I +CA$$
where $S$ is savings, $I$ is investment, and $CA$ is the current accounts surplus. 

The book then states "any domestic savings not absorbed by domestic investment must be shipped outside the country in the form of goods and services." I can understand how this works from an accounting equation point of view, but intuitively it doesn't seem to make sense. It seems odd that saved money would end up in the form of exports.
This is accountancy and double-entry bookkeeping, but intuitively there are two ideas underlying this:


The net difference between domestic investments and domestic savings has to be financed from abroad (or leads to financing foreigners if domestic savings exceed domestic investments) and this is reflected in the financial or capital accounts of the balance of payments.  Put more simply, if you want to build new buildings or buy new machinery or just put stuff into warehouses to sell next year, and your domestic economy is not saving enough to pay for this, then you need to get the extra stuff (probably represented in money terms, but really it is goods and services) from foreigners, creating new liabilities to them.
The financial or capital accounts should be balanced by the current account of the balance of payments (note the accounting use of the word balance). The net stuff you need for the excess investment over savings needs to bought from abroad (or if savings exceed investment then this needs to represent net stuff sold abroad).


There is a subtle difference between the balance of trade and the current account balance, with the difference representing income flows on existing international investments, but this is often relatively small and in accountancy terms is taken into account in the calculation of domestic savings.