Sculpt using tool symmetry

Tool symmetry lets you sculpt on one side of a model and affect the vertices on the opposite side of the model at the same time.

Select a sculpt tool from the Sculpt Tools tray.
In the Properties window, set the Mirror property to the desired symmetry setting.
NoteIf you have a symmetrical model that is posed asymmetrically, you can still mirror sculpt or paint strokes by setting the tool Mirror property to Tangent. To determine which axis the tool mirrors across, you must first define the topological axis. See Set a topological axis.

Notes on using tool symmetry

Tool symmetry may not keep the tool strokes 100% symmetrical after extensive sculpting. This is true for all live tool symmetry implementations for high resolution editing. If preserving symmetry is critical in your project, use layer symmetry instead.
When using tool symmetry with stencils, the primary tool and its reflection will likely scrub over different parts of the stencil image, so the result of each stroke will be asymmetric. If preserving symmetry is important to you while using stencils, use layer symmetry.