There are several ways to assign a card:
1. Assign a Card from the None field
If a card is not assigned upon card creation -> click on the None field at the top right side of the card to open a drop-down menu with all users in the board -> select the username.
For convenience, your username always appears as a second choice.
2. Assign a Card from the card Context Menu
Click on the card context menu -> select Assignee -> a drop-down menu with the users in the board appears. Select the username you want to assign to the card.
3. Assign a Card from the Card Details
Open up the card -> click on the Assignee field to open the drop-down menu with the users in the board. Select the username you want to assign to the card and update it.
4. Is it possible to assign multiple users to a single card?
In the Assignee field of the card, you can only assign one user (1).
The system allows you to add more card participants/contributors via the custom field of type: "Contributor" (2).
To visualize the second assignee on the card -> add a Custom field of type Contributor (follow the link to find a step by step tutorial on how to „Manage Custom Fields“).
Once the Custom field is successfully created, open the card and click on Add field -> Click on the "Contributor" custom field to add it to the card -> click on None and use the drop-down menu to select the user you want to assign as a second contributor to the card.
If the custom filed is mandatory for the card it will become available with the card creation.