The Zbrush ‘viewport’ is essentialy a canvas such as you would find in a 2D paint program such as Photoshop. Zooming in on the canvas will give you pixelated results.
When modeling 3D tools you can transform the model (zoom, rotate, move) using two modes. Transform mode gives you a handle called the Gyro for transforming the model. Edit model uses keyboard and mouse clicki combinations to transform the model.
In the Help menu look under Modeling 3D Objects > Basic Transformations and Modeling 3D Objects > Edit-Mode Transformations for a description and zscript tutorials showing how to accomplish transformations. There is also a nice hotkey sheet under Zbrush Essentials > Hotkeys & Mouse Actions, which shows the various Edit Mode key + mouse actions.
Hope that helps.
Edit: I’m far to slow today.