I’ve seen that it’s possible to move by holding down a direction instead of just tapping; how can you do that?
In Candli, there are two types of actions: instant and continuous. An instant action is triggered as soon as the condition is met, and only once. A continuous action is triggered as long as the condition is met.
In movement, the “add speed” action is instant, whereas the “apply force” action is continuous. If I understand your question correctly, this is the right action.
Note that in this case, there must be friction between the object and the ground or air friction, otherwise the object’s speed will increase indefinitely as long as the condition is met.
The “Movement” page of Candlipedia explains all this in detail.