On receiving your plant, open as soon as possible, bearing in mind that it could have been in the dark for up to 24hours. Do this even if daylight has passed, to allow the plant recover and breathe. If in a cardboard box, open or cut away the base (heavy end) such that the plant slowly drops through on lifting the cardboard up and over it. Alternatively, carefully open one side of the box, again from the bottom up, and along the seam, avoiding damage to any stems or branches. Smaller plants will sometimes be packed in bubblewrap inside a courier bag. Open these bags carefully to avoid any damage to the plant inside. 

During hot weather, water your plant daily until planted, but ideally plant as soon as possible into open ground, or a larger container. As for any planting, dig a hole larger than the container (deeper and wider), put the soil to one side, and mix it with an equal amount of peat, or peat-free compost. Use this mixture to surround the roots, making sure that the top of the root system is at ground level. You must avoid burying so deep that you cover any of the stem. If planting in a container, simply use the same compost/ soil mixture and make sure you have adequate drainage (a layer of gravel in the bottom of the pot should be fine).

You must water any plant as necessary, not too wet, not too dry. Bamboo plants in particular can get very dry in hot weather and warm winds. Likewise in cold, frosty weather, watering may be necessary with containerised bamboo, and even those in open ground. Plants generally only suffer or fail due to too much or not enough water at the roots. Evergreen plants in containers can hold water much better during drought than deciduous ones, so water accordingly.