Post on Instagram from the PC is not available. You can like, comment and share the posts but posting facility is not available on PC. You can share it only on app with these steps:
1.Download the Instagram app, open it and log in to your account.
2.Tap the plus sign button in the center at the bottom.
3.Now choose a picture, you want to post.
4.Crop the picture.
5.Instagram provides the filter options that you can change the look of your picture.
6.Now write down about your post or write anything you want to share with your friends.
7.Tap ‘tag people’ and pick the users whom you want to tag by searching them.
8.Select the location based on your picture.
9.Tap share at the top and right to the caption.