Hi Shaik, I'm not sure what you are trying to do. LAS files store lidar data. Are you wanting to create breaklines or other features on top of lidar data stored in a LAS file? If so, have a look at this help topic: Creating a LAS dataset—Help | ArcGIS Desktop. If you're asking how to create a LAS file from xyz data, this thread may be useful: How do I create a simple 3d model using xyz or las files.
If it's a small area, you could create a last return DSM from the lidar using the Local Government 3D Basemaps tools and use that to create building footprints in 2D in ArcGIS Pro. Then use the tasks in theLocal Government 3D Basemaps to make the buildings 3D. You can also use the tools in Local Government 3D Basemaps to create 3D Trees as multipatch polygons or use the Trees from Lidar tool to create points with 3D attributes to support the Add Preset Data - Realistic Trees. With Trees from Lidartool, it creates a all high points featureclass that has all the high points extracted.
If you have large volumes of buildings to collect, I suggest using Classify LAS Buildings tool on the lidar (if it is not classified for buildings). Then use the building extraction tools for creating 2D buildings and make them 3D using Local Government 3D Basemaps.
