Refer to your TV' manual, or Sharp support, for help. It's also quite possible that there is no "App Store" in the way you know it from Apple/Google/Microsoft.
I have the model up It a webpage/searchpage based platform all and freaking awesome!! All sharp Smart TVs have it now even when you posted this. Do you have the en2a27st remote if so hit HOME KEY scroll to the right so you see VEWD APP STORE & you can go from there.. they don't have a ton I think 1500 apps or so right now but it's a completely different and new type of App Store so more and more Developers will make they're app available. Once more people learn how to create on it etc .. but great all in all . The first time I found it though before vewd came about what runs on I believe Android now, was when I opened the browser and there was a factory type homepage or section on the page u had to go to ..