The knives on this site are predominantly made from carbon steel, not stainless steel (more the sort of thing used in a precision tool than a knife and fork). This means they take a bit more looking after than regular cutlery. A carbon steel knife will rust - and quickly - so don’t leave it wet. Wash it carefully (it’s very sharp), dry it, and ideally put a little food safe mineral oil on it (the sort you’d use for a wooden chopping board). Never put it in a dishwasher. If you even think about putting it in a dishwasher, apologise to your knife immediately, or it’ll never forgive you.
The pay off for all this care is a blade that’ll be sharper than any stainless steel knife, it’ll hold the edge longer, and it’ll be easier to sharpen. Acidic food will change the look of the blade. This is completely normal. A patina will build up and tell a little bit of story of how you’ve used the knife.
When the time comes to sharpen the blade, you could get in done professionally, you could teach yourself to sharpen with wet stones, or - in a pinch - you could use one of those handheld devices with little ceramic wheels/rods (just don’t tell me). Don’t use the knife on glass or ceramic cutting boards; wood or plastic (HDPE) is best. The knife will stay sharp for much longer.
One more thing - if the knife has been etched to a dark colour, this will slowly wear off with use. Just something to be aware of when making your choice.