Moving $CKB and other assets from Layer 1 to Layer 2 is done using a special L1 deposit address that users will send their assets to, which is then picked up by L2 validators to complete the deposit. This deposit process is fast, and usually does not take more than a few minutes.
At present time, the deposit address must be generated using a dapp. Users of the popular YokaiSwap will find that everything they need to move $CKB from L1 to L2 is available on the YokaiSwap website. This is the recommended way to handle this action since wallet support for L2 is still being developed.