To put both tubes into the simulation as separate objects you have to put them into two primitive groups, by hand or procedurally (see Group SOP). You can see what group you have by MMB on any SOP. In DOPS you use RBD Glue Object with Internal Glue strength set to zero, and you have your two objects separated.
I strongly recommend you to start with tutorials. Houdini is easy after you open you mind for its basic workflow.
You can always use shelf tools to create your DOPS simulation.
1) Create two tubes by shelf button (Create Shelf) and place them in viewport (use ALT to place them in Y axis)
2) Select one of them and use Shelf tool “RBD Object” (Rigid Bodies).
3) Do the same with second tube (actually you can select both at once)
4) Add Ground Plane (from the same Shelf)
5. Play!
Done.
I counted: six (6!) clicks and twice ALT key. Can't be easier.
hope this help!
sy.
EDIT:
I edit you scene. All I did:
I added group SOPs to place boxes in separate groups
I changed RBD Object for RBD Glue Object which uses primitive groups to define object's parts (so setting internal glue at 0 effectively creates many objects).
All the rest is fine