In the card, participants have specific roles:
owner;
member;
responsible member.
The card creator and other users can invite participants to the card and assign these roles manually.
However, it is also possible to automate this work in FlowFast:
By default, a user who has created a card in the "In Progress" or "Done" column types is automatically added as a participant to the card and becomes a Responsible member.
You can also set a user who has moved a card from the "Queue" to the "In Progress" or "Done" column type to be automatically assigned as Member (or Responsible member)
In this case if a card is moved to the "In Progress" or "Done" column the person who made the move becomes the card Member, and if the card has not yet been assigned a Responsible member, the person becomes one.
You can set this up by setting a rule for the board:
Click on the three dots in the top right corner of the board;
Select the "Rules" option;
Check the box next to "Automatically assign the author as a member ..."