You can delegate tokens to a validator using the following command:

./hmy --node="https://api.s0.t.hmny.io" staking delegate \
    --delegator-addr [ONE ADDRESS] --validator-addr [ONE ADDRESS] \
    --amount [AMOUNT] --passphrase

./hmy --node="https://api.s0.b.hmny.io" staking delegate \
    --delegator-addr [ONE ADDRESS] --validator-addr [ONE ADDRESS] \
    --amount [AMOUNT] --passphrase

Example:

./hmy --node="https://api.s0.t.hmny.io" staking delegate \
    --delegator-addr one1km7xg8e3xjys7azp9f4xp8hkw79vm2h3f2lade --validator-addr one1km7xg8e3xjys7azp9f4xp8hkw79vm2h3f2lade \
    --amount 10000 --passphrase

The CLI will ask for the passphrase for the delegator-addr keystore file.

--delegator-addr is the ONE address of the delegator (string)

--validator-addr is the ONE address of the validator (string)

--amount is the number of ONE tokens to delegate to the validator (float)