Instagram was made to share pictures and videos from your mobile phone. But you can use all its mobile features from your computer, too.
If you're using a Mac with the Safari web browswer, go to "preferences" and click "advanced." Then go to "user agent" and select Safari, then iOS 10, then iPhone.
Now you can use Safari like your mobile phone. The camera button should be at the bottom of the page.
PC users with Chrome have it a bit easier. Just right click anywhere on the page, choose "inspect" and click on the tablet icon.
Want to watch your friends' stories? Just install the "Chrome IG Story" extension in Chrome.