Select the currency you'll be exchanging from on the left, so in this case ASTER, and the one you'll be exchanging for on the right, in this case MNT.
Input the amount of ASTER you want to sell for MNT, paste the receiving address for your MNT after the trade is done and click "TRADE".
Finally send the amount of ASTER to the address that shows up on the screen by either copy-pasting the address shown on the page into your wallet or scanning the QR code on the right.
Sit back and wait
Make sure to note down the Trade ID shown on the page in case of issues with the trade.
Transactions can take a while to complete (often as long as an hour) so be patient.
If you encounter any issues contact Intercambio.app customer support with your Trade ID.