Well If your asking what it does on Pokemon platinum It makes the foes pokemons hp go down to 1... most of the time.
Once you get to Veilstone city, there is a TM floor(floor 3) then you go and ask the people at the desks and one of them will give you false swipe.
some Pokemon like scizor learn it there is no TM for false swipe.you can catch a scizor with false swipe on the route you unlock after beating the elite four in diamond pearl and platinum.
snowpoint temple and you have to have Regirock, Registeel and Regice in your party and a guy that knows False Swipe.
There are many Pokemon that can learn false swipe: Scyther, Marowak and many more.
To teach Smeargle False Swipe you need to find a Pokemon to fight that knows False Swipe. Make sure Smeargle has at least one copy of the move Sketch. During the battle with the Pokemon that knows False Swipe use Sketch after the opposing Pokemon uses False Swipe. If done correctly your Smeargle's Sketch should permanently turn into a False Swipe.
i have platinum so I'm not sure but you just buy it in veilstone
false swipe is learned by the following Pokemon upon levelling:scythernincandazangoosefarfetch'dgalladegrovylecubonehowever, false swipe is also a TM. this makes the move available to other Pokemon as well (kriketune, weavile, parasect, kingler, anorith, etc).
After you've seen 25 Pokemon or more, talk to Professor Juniper and she will give you the TM for false swipe
The Pokemon tha has false swipe in Pokemon diamond is Shedenja
Zangoose.
absol and sceptile
Marowak and Scyther.