I have some questions related to the different layers of Altium:

• Top Solder: Is the soldermask keepout, or soldermask expansion. It is a zone in which there is no epoxy. The epoxy is used to protect the circuits.
• Top paste: Is the paste in the stencil. It needs to be removed in the test points for example or in areas you would like not to have it.

The solder mask expansion: is the difference from the copper and the pad. Is a empty space. This ensures that there’s a reliable and suitable area for soldering while also preventing solder bridging between closely spaced pads.