This is more of an important basic knowledge. There is no difficulty in exchanging items. Notice how to do the following:

1) Select the character/friend, by clicking on it, with whom you want to exchange items and press "Swap". You can also simply accept the exchange request sent by someone else;

or you can accept a friend's invitation.

2) Once you have accepted/sent the exchange request, position the items/money you wish to exchange;

3) Now, simply press "Swap" so that the selected items, as agreed between you, become part of each player's inventory..

Be prudent in trading! Never exchange your items before checking all that offered by the other party.