While you can create and view hashtags on the instagram app you can’t view hashtags on the instagram.com website.
There are a bunch of limitations on how you can interact with your account via the instagram.com website – it doesn’t offer all the features of the app. It’s very confusing since many other online services (like Facebook) offer full functionality on both website and app.
You can see lots of notes about how to use the API that show you ways to display hashtag-sorted images yet instagram.com itself doesn’t offer any way to view by hashtag. “Hashtag instagram” is a very popular question online but the answer is confusing if you are not on the app.