Your knife is carbon steel, not stainless steel. This means it will rust if not cared for and kept clean.
When you leave our workshop it will be shiny and new. If you want to let it develop a grey/black patina then do nothing. To accelerate that process then paint it with mustard, leave for a couple of hours then rinse off and dry.
Oil the Knife
The best way to ensure your knife stays looked after is to keep a thin layer of oil on it in order to keep the moisture off. You can use a good food grade mineral oil to apply to the blade, vegetable oils tend not to work so well and go sticky over time. You can also use this oil on the handle to protect and preserve it.
Rust
If you see rust bloom starting to form on your blade then don’t panic! You can use fine sandpaper to remove them (1000 grit minimum) or a nylon pot scourer/ fine steel wool.
Beware the Dishwasher
Never, ever put your knife in the dishwasher. This is the quickest way to bugger a knife (this includes stainless kitchen knives with handles). The high temperatures degrade the adhesive binding the handles and bolster along with the different expansion rates of the steel vs handle material. Eventually your handle/bolster will just pop off (not to mention fade and look rubbish).