engine swappin

what exactly do u do when swappin an engine from one car to another. if u do a swap, do u need to take out absolubtly everything out from the old engine and intall the other engine with all its components? do u need to make mods to the chassis and other stuff so that it will work perfectly with teh new engine?

It all depends on the engines, what car they came from and where they are going.
The most simple is to swap the same size of engine from the same make, model and year of car. Disassembly is kept to a minimum and everything should hook up easily because the old and new engines are identical.
Anything else ususally, but not always, involves modification to make it work. The only way top know for sure is to provide more information about the make, model and year of car and the engine you want to swap.