Astar is the network that aims to be the parachain of Polkadot. Shiden is the sister network of Astar which is the parachain of Kusama. Basically, Astar and Shiden share the same code base. The biggest difference is the economic impact. As there is a huge difference in economic value between KSM and DOT, Astar and Shiden will have the same relationship. However, as of writing this tutorial (October 2021), Polkadot parachain is not available. At the current development stage, we can only use Shiden.