Hi Daza - there currently isn't any concept of holding objects (besides items in your inventory), but it is something I may explore down the road.
In regards to lighting, there are a few different types of lighting you can currently adjust in your map. Under the map properties on the left, there is an ambient light, which is basically the overall global lighting for the entire map, and a directional light, which simulates the sun. With the directional light you can adjust the angle, color, brightness, etc from the properties panel.
Also, besides setting objects as "light sources" from the Voxel Editor, you can also add extra positional lights to the scene in the Map Editor's Edit Mode by right clicking an object or tile then selecting "Add Light". This adds a light at the location of the selected object. The light will show up in the properties panel, and from there you can tweak settings like position, color, etc. Hopefully that is helpful!
Godot also supports spotlights which can be used for things like flashlights, but I just haven't gotten around to implementing those quite yet. I also plan to add some scripting functions later on to let you dynamically adjust lighting.