Can anyone say what's the difference between loft and skin node in houdini.

Skin :Builds a skin surface between any number of shape curves.

Loft :Builds a skin surface between any number of shape curves in one direction.

Please explain.

Skin can create NURBs surfaces or polygon surfaces. I don't see “Loft” in H14 or H13 so I'm guessing you mean PolyLoft, in which case that's a polygon only SOP, you won't be able to have a NURBs surface.

if it's about Loft and Skin shelf tools then note that both will use Skin SOP, but

Loft - connects curves only in one direction (u)
Skin - connects curves in 2 directions (u, v)

in other words:
Loft Shelf Tool uses only 1st input of Skin SOP
Skin Shelf Tool uses both

more here:
http://www.sidefx.com/docs/houdini14.0/shelf/loft [sidefx.com]
http://www.sidefx.com/docs/houdini14.0/shelf/skin [sidefx.com]
http://www.sidefx.com/docs/houdini14.0/nodes/sop/skin [sidefx.com]

thx.

The Shelf?! I'd completely forgotten about that!