After using the feature, a set of transactions will be held and the amount you've input will be sent to your on-chain balance and deducted from your lightning balance.
A portion (most) of that amount will be added to your inbound capacity.
For example if I want to make my inbound capacity 0.002, I need to pay that much?
Yes and that must be in your lightning funds' outbound capacity, not on-chain.
But you're not actually "
paying" that amount, it will be sent back to your on-chain funds, you'll only pay the service fee.
The fee, I think it's about $4 equivalent and the on-chain transaction fee (
let me find a reference).