hi guys.

Can anyone simply explain how can i create a particle system which emit from a specific geometry?

hi,
have you seen the tutorials for the particle system?

http://www.sidefx.com/index.php?option=com_content&task=view&id=2574&Itemid=389 [sidefx.com]

http://www.sidefx.com/index.php?option=com_content&task=view&id=2635&Itemid=389 [sidefx.com]

Thanks mandrake

Hello Mahdi and welcome to the Houdini Forum.
This forum is awesome and you can take your answers very quickly in this place :wink:

About your question , it's really simple !

Just select your geometry and use “Source Particle Emitter” tool in the Particles shelf.

But you can do this with “POP Network - old” too.
in this case :
Append a “POP Network - old” node and connect your geometry to the first input.
then append a “Source” node in the POP Network and set “Geometry Source” parameter to “Use First Context Geometry” , Also I suggest you set “Emission Type” parameter to “Surfaces Random” 8)