When you sign into the portal you will want to select the mSign product on the left. It will be the orange icon.
From here you want to make sure Documents are selected. Then select the Create button on the top right.
From here you will be asked to upload your document. You can choose to upload from your device, from the cloud, or start with a blank page. You can also choose a saved template.
Once you have your document selected you will select the Next button. You have now created a document and can start adding fields.