How can greater savings lead to greater investments in an economy???

Suppose planned savings are higher than planned investments. It means that the households are not consuming as much as the firms had anticipated. In other words, planned output is greater than planned demand.
As a result, producers see a rise in their inventory level, beyond the planned level. To bring back inventory to the planned level, producers cut down the production. This reduces aggregate output. The process continues till the aggregate demand equals the output produced in the economy, i.e., planned investments becomes equal to the the planned savings.