Can someone explain Instagram to me 😂

I made an Instagram a few years ago because my friend wanted me to, but I think I only posted 1 or 2 things and then never went back on.

I got the message to be a Glow Ambassador so I figured since I already have an account I may as well link it. After I entered my tag or name, whatever it's called, Glow said to "share this to I Instagram and tag GlowHQ" but when I clicked the share button it only opened up the option to pick someone to send it as a message to? Is there no way to just share it to everyone on my page? When I tried to get out of it, there's no other way to get back to the post it wanted me to share... I feel old asking 😂 but I'm so confused on how it all works! Is anyone able to help me?