Door handles are finicky things to fit, but if you're careful you'll be fine!
Mark the height that you want the door handle to be on and then on the outside of the door, using a flat drill bit drill a hole large and deep enough that the latch body can slide completely into the door.
Slide the latch body completely into the door and then mark around the latch plate with a pencil.
Chisel out the inside of this rectangle so that the plate sits completely flush with the door. Make sure not to chisel this recess in the wood too deep.
Hold the latch piece against the outside of the door, level with the hole you’ve just drilled, use it to measure out the correct distance for the spindle hole.
Mark up the position for the spindle hole with a pencil and drill the hole for the spindle making sure to use a drill bit larger than the spindle.
You should now be able to slide the latch into the door and slide the spindle through the spindle hole.
Screw the latch plate into space using the small woodscrews provided with the latch.
Slot the door knobs into place and then screw them onto the door with small woodscrews.
Finally you will need to attach the strike plate to the doorjamb. Mark out the correct height, draw round the strike plate and chisel a small recess for the plate to sit in, before screwing it into place.
Of course, if you can't be bothered this is an easy job for a handyman or even carpenter, so post your job today to get quality businesses to contact you to quote.