**Never** use the dangerous unverified import option, it is strictly for experts only. Especially, don't use it with any blockchain you download from the Internet, including the official site. It is only safe to use if a) you are importing a file that you exported locally, yourself *and* b) you are absolutely sure it was already fully and properly verified before exporting.
Download the Current bootstrap from https://downloads.getmonero.org/blockchain.raw; you can skip this step if you are importing the blockchain from another source.
Most people don't need this. To use Monero, just start the software and it will synchronize itself with the peer-to-peer network. Normally, this is much faster than downloading and importing the blockchain as detailed in this guide. This is because you'll be downloading from many peers instead of just a single server, and the Monero @daemon will verify each block as it's received, instead of verifying separately after downloading.
