gravity load in BuildingTcl

[sisa]

hi!
I've just started to practice Building Tcl...I find it very usefull and practical but I've some problemy with loads.
1) I dont' understand if the gravity load is a concentrated or a ditributed load. When I define the elevation model I can put gravity load on the beam so I think it is a distributed load...but there is also a sign (an arrow) on the column: what is this? a concentrated load?
2) if I would put a concentrated load on the column I have to assign the relative distributed load on the beam or I can put it on the column directly?how?
3) am I obliged to assign a gravity load in order to make the analysis? If i wouldn't consider gravity load can I put it zero? how?
I hope someone can help me also just in some of this question beacuse there are very few suggestion online...
thank you
Annalisa