What is the Paint Height tab?

Hi, i’m just starting to learn unity with tutorials online. Can someone please explain me what is the meaning of the Paint Height tab?

I know its a basic question but i can’t really see what it does.

Thanks

You should read the documentation about the terrain tool.

The second tool from the left, Paint
Height is similar to the Raise/Lower
tool except that it has an additional
property to set the target height.
When you paint on the object, the
terrain will be lowered in areas above
that height and raised in areas below
it. You can use the Height property
slider to set the height manually or
you can shift-click on the terrain to
sample the height at the mouse
position (rather like the “eyedropper”
tool in an image editor). Next to the
Height property is a Flatten button
that simply levels the whole terrain
to the chosen height. This is useful
to set a raised ground level, say if
you want the landscape to include both
hills above the level and valleys
below it. Paint Height is handy for
creating plateaux in a scene and also
for adding artificial features like
roads, platforms and steps.

Documentation here