It was not possible earlier to post on Instagram from a computer or PC directly. But, you could use some alternatives like a third-party app or Google Chrome extensions to post on Instagram from PC. If you are lucky, you can post on Instagram from your PC without the help of an external feature because Instagram lets some of its users post from a computer. The feature is not added to the iPad yet. Now, how to post on Instagram from computer, you ask, the answer is, as you post from phone.