You either need to be an Admin of your organisation or be added in the document that your colleague is working on in order to view it. The account admin has to share the rights of the document with you in order for you to have access as a normal member. Therefore, if you cannot see the document you are supposed to be working on, check the admin's account first to see the sharing rights of a specific document.
For instance, in the picture above, Samyak Nakarmi and Ram Bahadur are the signers of the document as their signer button is turned on. And since Sriyanka Nakarmi's signer/approve button is turned off, she is not involved in the document but can view the document.
You can find the documents that you are added to or own in My Documents - you can find this folder in the left panel.
Please let us know if you have any questions. Feel free to reach out to us at email@example.com or via our app's live chat.