Smooth transition are automatically handle by Millumin. You just have to specify the time of its duration to create one. The fisrt step is to activate the edit mode in the dashboard.
Then, for the column you want to set an enter transition, open the column panel.
And set the time for the transition you want.
Now, each time you launch the column with the transition set, Millumin will automatically launch a transition with the previous column.
You also can modify the shape of the transition's curve from "Ease in/out" to "Linear".
If you have many layers, maybe you want to set a different transition for each. So, you have to activate the "media transition" property in the property panel.
And then, just set the time you need for your transition.
Now, the second layer has a shorter transition time.
Note that in this mode you could personnalize your transition's curve. For exemple, in free mode, you can adjust the delay before beginning the transition of the previous media. You also can set independently the transition length of the previous and current media.