Goods issue from multiple location

Hi

The scenario is i have 1 plant and 3 warehouses, The material can be stored at any one of the warehouses. The sales person is creating the sales orders and they are not aware from which warehouse the material will be dispatched.

If i create one plant and 3 storage location and 3 warehouse in SAP, how will system will carry out the availblity check of the stock and do the delivery and PGI

Pls suggest the best method to be followed in such process.