Witness basic duties and playing with cli_wallet are not in the scope of this episode and you can find it already on a various tutorials, but from a point described here it's fairly simple: first of all to get cli_wallet you need to build it (above builds only steemd), then run it, set your own password, unlock a wallet, import your active key (required for updating witness parameters), then update with
update_witness "witnessid" "https://steemit.com/" "STM1111111111111111111111111111111114T1Anm" {"account_creation_fee":"0.100 STEEM","maximum_block_size":65535,"sbd_interest_rate":0} true replacing witnessid with your id and that null public key with your own public signing key.
At some point I will release some post with witness 101 and exchanges 101 but for now you need to go through other tutorials that cover such subjects.