I am not able to find a way from where i can create opportunity, company, opportunity roles . While i am able to create it using the API calls but not able to find any opportunity at the UI.
Could you please let us know or it would be helpful if you will provide screenshot from where i can create opportunities at the UI or get all the opportunity info.
You cannot create opportunities in the UI. YOU can only create them from the CRM or from API, but the API will only work if your Marketo is not sync'ed with Salesforce or MS Dynamics.