Right click on the layer or click on the paint mask icon at the bottom of the layer stack to add a paint mask to the selected layer.
Adding a paint mask will bring up the brush panel, allowing you to directly paint a mask onto the layer. For more information, see Painting.
This panel contain all the brushes a user have. Custom brush and those downloaded from Megascans library are shown here. You can select your desired brush start using paint mask.
Size: Increase or decrease the size of your selected brush
Spacing: Set the spacing between successive brush marks within one stroke.
Angle: Set the angle of your brush you want to paint with.
Opacity: Control the transparency or strength of the brush.
Flow: Control the rate at which the brush paints.
Softness: Vary the radius of the maximum intensity.
Center curve: Control the curve along the brush.
Base curve: Control the curve along the base of the brush.
Size Jitter: Adjust the jittery effect produced by the brush.
Angle Jitter: Change angle of the jittery effect produced by the brush.
Flow Jitter: Adjust the speed of jittery effect produced while painting.