As David mentioned, you download skills from the Digital Exchange. Your Blue Prism Portal login should give you access to the DX. Once there, download whatever skill, VBO, etc that you're interested in. Once you have it, you can import it into your BP environment by starting your BP app and going to File -> Import... Once you have a skill imported into BP, the skill toolbar will be visible in the Process Designer on the right side of the screen.
Cheers,
Eric