hey man, bitsquare has no wallets for other coins. there is only an internal BTC wallet.
You need to create an "account" so that the other party knows where to send funds to.
Under the crytpocurrency account section, all you need to do is provide the XMR/altcoin address that YOU CONTROL.
In your case, you want to sell XMR.
When someone takes your XMR sell offer, you will need to transfer the XMR from your separate/external wallet you control, bitsquare will tell you the other parties XMR address to send to. When the other party manually checks their XMR balance in their wallet, they will then mark in bitsquare as funds recieved. Then multisig BTC escrow is unlocked and sent to you.
Hope that makes sense.
for you and others..the faq covers a lot of details how it works. check it out if you havnt.