I was raised on Opinel knives. They come in different sizes; I think the biggest one we have is #10 but before the whole country went mad with paranoia I kept my #6 in my purse, mainly to cut fruit, but also to whittle if I was bored, cut twine, and in case I had to walk through a dark parking lot or something. (Yes, they are French. I’m not going to apologize. After all, I taught French for 12 years. I like to be able to cut up delicious baguettes, camembert, and saucisson.) They make a nice simple folding knife which is very affordable, has a nicely shaped simple wooden handle, and the blade takes a very nice edge. My father said the steel was a little softer which is why it takes such a nice edge. (A stainless steel one might not be as easy to sharpen.) Low-tech but perfect.
To open, tap the back end, which has a little flat point just for that purpose, and the tip will pop out of the end, so you can open the knife. When it is opened all the way out, turn the circular piece of metal (hasp, tang, whatever you would call it) to lock the blade in place. When you finish using the knife, wash it if necessary and fold it back up when dry. Like any pocketknife/folding knife, if you fold it up encrusted with blood and guts, it will be nasty and maybe hard to open next time you want to use it. Obviously with a handle like that you don’t want to leave it soaking in water for days. Respect your tools and they will perform for you. Oil it occasionally with olive oil.
To sharpen, see Sharpening Your Knife.
They come in different sizes and also with different handles. My husband got one with an olive wood handle in Andorra. It has always stayed very nice. I like how the handle fits my hand.
This is the knife I use for butchering and meat processing, along with my big old Chinese cleaver.