There's a range, and quite frankly I can't find a lot of groceries I want at Walmart. In most major cities, you're going to have a few different 'levels' of grocery store:

1) The big chain grocery store. HEB in Texas and parts of the south, Cub or Kroger in the North, Piggly Wiggly, etc. These stores carry a large range of fresh produce, generally have butcher, bakery, and cheese departments with people working in them and often a deli or some other 'prepared hot food' as well. Large freezer areas, canned foods, baking goods, etc. Everything you would need generally speaking, and a large selection ranging from 'no name' budget goods to brand names and some organics. As far as I understand shopping in Northern Ireland (not much!) take a Tesco Superstore, multiply by 2.

2) Discount smaller stores with a lot of store brand goods. Trader Joe's, Aldi's, that sort of thing. Less of a selection, less choice, don't always have everything you need but MOST of what you need. Often some very good seasonal or specialty stuff. It's rare that you could get all the groceries you need JUST going to these places, and often their fresh produce and meats are more expensive than bigger grocery stores, while their pre made frozen food, things like cereal and snack food are cheaper.

3) Bodega's, corner stores, mini marts. These are more in urban areas, where people may not always be using a car. A small selection of most needed items to pick up when you need them.

4) Luxury supermarkets. Whole Foods, Lunds & Byerly's, Kowalski's, Harris Teeter, Erewhon. These are going to carry a lot more organic goods, upmarket brand names, generally less frozen and canned foods. You're going to have professional butchers, cheesemongers, bakers, florists. There'll be things like olive bars and made to order sandwiches, and often bakeries that can make wedding cakes. Specialty baking ingredients, international foods you might not be able to find at other stores. There'll be carpeting, and nice lighting, and thought put towards attractive displays of goods. The expensive stuff is expensive at these places, but the cheap stuff is more expensive at these places than the stuff you can get at any of the other choices.

5) Grocery stores as part of big box stores: This is your Wal-Marts, your Target Superstores, etc. Yes, they have groceries, and a lot of them, but not as much as a big chain grocery generally speaking. Grocery is not what they focus on, it's a side hustle for the other things they sell. But, in some areas, especially exurbs and rural, it might be the the only grocery store.

And of course, especially in urban areas, you'll also find your butchers, spice stores, bakeries, and other specialty stores.