Instructions on the care of each species or hybrid purchased are most always included with the sale. Growers can also answer your specific questions concerning your new plant. At a discount store however, you may purchase an orchid and in some cases, not even know what species or even genera you are buying. Because each genera and, in some cases, species within a genera, may require very different environments to thrive. The answer is, you can't.
Shippers often repot the orchids just before shipment to the stores.
The problem with this practice is twofold. Repotting is often traumatizing to well establish plants, frequently damaging their root systems in the process. Customers love the pretty paper, so they do not remove it after purchasing the orchid. The paper causes the already saturated shipping medium to become water logged because there is no way for the excess water to drain away. As you can see, your bargain orchid has been through a lot before you happen to walk by it in the store.