How to apply Floor Live Load in Staad

You can apply them as floor load on closed panel. You can use either range options or group options to pick the beams subjected to this loading. Please refer help file for more details.

file:///C:/Program%20Files/Bentley/Engineering/STAAD.Pro%20CONNECT%20Edition/Help/STD_FLOOR_LOAD.html

You can learn to add loads and load combination through this Ondemand videos,check on the link below

https://learn.bentley.com/app/Public/ViewLearningPathDetails?lpId=111706&callFrom=MyLp&aftkn=e986c68c-0b0e-4ff8-b42a-68830085b463

It is helpful,when i started learning StaadAbhisek M

and their team advised me to sign up and i was able to access Ondemand videos which shows 

1.Step by step on how to model structures

2.To assign member properties

3.Modelling loads and load combination

4.Designing of structural elements.

Just take time and pass through the videos you will have more knowlege about Staad