How do I add heroes to my party?
See the Adding, Removing, Swapping, Heroes chapter. A hero can be added or removed from your party when a text box is displayed. Go to the Edit Conditional menu of a text box, and find:
never do the following do not add/remove heroes
and use the left and right arrow keys to change it to:
always do the following then add heroname to the party
Then, when this text box is displayed, the hero will be added to your party. In most cases, you want to attach it to an NPC who uses the same graphics as the hero you are adding, and is one-time-usable. The text box might say something like "My name is whatever. I want to help you in your quest"
There is also a command for adding heroes with a plotscript. See the Plotscripting Dictionary. You might also be interested to know that there are plotscript commands called "swap out hero" and "swap by position" which can help you to decide in which order your heroes are going to enter the party.