(This feature is in development.)
You will need to use the Writing Desk, which is currently located in Mrs. Hatch's parlor. (We intend to include portable writing desks in the future.) Left click on the writing desk at the back of the room to open the Writing Desk window.
In the Writing Desk interface, you will see buttons for "Write Invitation" and "Respond to Invitation".
You can invite another person to a number of events, such as a ball or even a simple walk. Click the Write Invitation button. Your stationary will appear with a list of your acquaintence names. Click the name of the person you wish to invite to choose them.
Next, choose the event you'd like to invite them to attend with you. You can use the mouse wheel, if you have one, to scroll through the list or drag the scroll bar on the right side of the list.
Now you must select your prefered date and time for the event. Click on the line of the calendar corresponding to the date and time of your choosing. To show the day in your local time (in addition to the early 1800's) click the watch icon on the corner of the calendar show in the screenshot.
You may send the invitation as is or add a location to your request.
The event is now in your Calendar, awaiting the other player's response.
Responding to an Invitation
Other players and NPCs can send you invitations to various events. If you have an unanswered invitation you can choose to accept or decline. Click the "Respond to Invitation" button to see if you have any new invitations.
If you accept and send your response to the invitation the event will be added to your calendar. (Note: There is a known issue that the gender is not being correctly updated in the invitation response letter. We fix this in a future update.)