there is a box on electrum receive page called
"requested amount" mBTC
I left it blank, is that correct?
as i said you only need a bitcoin address. and that tab is giving you one of your bitcoin addresses from your wallet to receive bitcoin in. but it has some additional options based on BIP-21 that generates an special bitcoin URI that contains bitcoin address, a message, the requested amount and some more additional information and is used for "requesting payment"
https://github.com/bitcoin/bips/blob/master/bip-0021.mediawiki