You need to use a Trigger, better just using a UIButton as its easier to mess with at the start.
Then in the Button Trigger tab, Add Click Action
Then it is just a case of selecting the Atom, then the Receiver, then the Target and then filling in what you want the bubble to say.
There is a BubbleLifetime you can select first, this dictates the lifetime of the SpeechBubble or ThoughtBubble.
Use it if the bubble disappears too fast to read or you want it up there for a while longer.
You have to create the Lifetime trigger action first, then have to create the speech bubble trigger action below it.
You can add them to most triggers, like the animation timeline etc to make them appear when you want.
And as you can see in my screens, there is no spellcheck for the speech bubble. XD