For your first question: technically yes, but it's not really the way it's meant to be done. If you want to pin something with storage, you can become a host on the Sia network and then make that content available through your host. But this also means the content is subject to going offline if you go offline (unless someone has re-pinned it to other hosts), and Skynet is really meant to be this high reliability platform where you don't need to worry about particular users going offline.
If you want to download skynet files using the command line, you can run 'siad' in portal mode as a daemon, and then use 'siac' to query the daemon. 'siac skynet download [skylink] [destination]' is the command to perform the download.
Doing it this way means you gain direct decentralized access to Skynet instead of needing to funnel through a portal.
Is there a way to be a host and then pin other people's content that I like? I'd love to be a host that pins public content without an explicit financial transaction.
If you want to download skynet files using the command line, you can run 'siad' in portal mode as a daemon, and then use 'siac' to query the daemon. 'siac skynet download [skylink] [destination]' is the command to perform the download.
Doing it this way means you gain direct decentralized access to Skynet instead of needing to funnel through a portal.