Adding transitions to slide LAYERS issue

Hi there, I am new to storyline tho I have experience working with articulate presenter. I am creating a presentation using storyline, and I need to add a transition to a particular layer on a slide. I did the tutorial online, and it said that: " To apply a transition to a layer within the slide, select the layer from the Slide Layers panel." 

I did that but nothing happen, and I couldn't even see the elements I had in that layer. 

I only have two layers in that slide, and the one layer I wanted to apply the transition to had grouped objects. I ungrouped them and apply the transition again, but I had the same result; nothing happened. 

Does anyone can help me with this?

Thanks a lot!!

Angela.