When creating a 3D character model, artists often create a neutral pose (sometimes called a T-pose) where the character is standing straight with arms outstretched. The reason for this is that it is generally easier to model this way using symmetry and with easy access to all parts of the body.
However, this neutral pose is not very interesting visually and when you want to show off your work you’ll want to pose your character so that it looks dynamic and lively.
ZBrush has several features to help you pose your model. You can explore them on these pages: