If you are using latest update in your phone of Instagram (Android|iOS) so you can do shopping from it.
How to do?
Search and Explore:
Just open your Instagram then go to search and Explore by tapping. On top of your screen just find and tap Shopping. One thing you can just shop any brands which you are not following also.
Feed and Stories:
So if you are following any brands on Instagram so you have to just tap upon it there you will see description after if you like then visit website to shop it.