The Store app is a typical Modern-style app, and that means it opens up full screen, and uses a tile layout with a bias for horizontal scrolling. If you've a mouse connected, you will notice a horizontal scroll bar across the bottom. Semantic zoom is fully supported, which lets you easily and quickly navigate from one end of the horizontal layout to the other.
Apps are grouped in easy-to-find categories such as Games, Social, Entertainment, Photos, Music & Video, Sports, Books & Reference, News & Weather, Health & Fitness, Food & Dining, Lifestyle, Shopping, Travel, Finance, Productivity, Tools, Security, Business, Education, and Government - that's a total of 20 categories! A few apps pertaining to each category are highlighted (and constantly refreshed) right on the main Store page, but you can also choose to browse each category sorted by top free apps and new releases. In addition, positioned at the very front of the Store is a category called 'Spotlight', which highlights some of the top apps across all the 20 categories. This Spotlight category has its own Top free and New releases sections as well.
If you prefer to search directly for an app, you can do so by using the Search Charm (provided you know at least part of the name).
What if you just want to browse apps in a particular category sorted according to their prices, or release dates? Turns out, there's a way to do this somewhat. When you hit on a category name on the main store page, you'll be brought to an app listing with a few drop-down menus at the top. From here you can sort apps according to their price types (all prices, free, free and trial, paid), and prices (sort by lowest price, sort by highest price). You can also 'sort by noteworthy' (we've no idea what's the criteria for this), ratings, and release dates. For categories that allow it (such as Games), you can even sort by their subcategories.
Selecting an app will bring you to its app page, which gives you an overview of the app, as well as more detailed information and any user reviews. You will also see the price and size of the app. If it's a free app, you'll see a 'Install' button. If it's a paid app, you'll see a 'Buy' button. Either way, before it proceeds to download the app, Windows Store will prompt you to sign in to your Microsoft account. If you're buying an app and haven't already linked a credit card to your Microsoft account, you'll then be directed to a page where you can enter your credit card information.