Leeks are an interesting vegetable resembling large green onions. Not only do they look like an onion, they do have an onion taste, but very mild. It's a great vegetable to explore, if you haven't done so already.
One thing to note is, there are a lot of layers to the leek and you need to be careful when preparing them. You will want to chop off the tip and any hard green stems. You may see some recipes that never include the green stem, but I always use the softer portions. I hate to throw out any part that is edible.
To wash, you will need to cut lengthwise and run it under cold water. Make sure to go through each layer to ensure that all grit is out.
This is truly a wonderfully tasting dish, one that you will want to try!