In short; Log-in on the app, click on the Instagram icon in the sidebar on the left. Enter your Instagram username, password and proxy (recommended), then save.
Adding your Instagram account takes less than two minutes and requires just a few steps;
1. From the main menu, click the accounts icon (in the left sidebar)
2. Click the add new account button
Enter your Instagram username, password and click the add account button.
You can also enter a proxy (recommended).
3. You might need to select a verification method, click on the send via SMS or send via email button and a verification code will be sent to you.
4. Enter the verification code in the box that comes up next and click on save changes.
Your account is now added to the app.
If you are facing a re-login required or verification loop, read how to fix it here.