To import a Model Asset into the Portal, a project must be created. So after creating your project select the project you want to import assets into.
The page will split and the bottom half of the projects page will show all the assets in that project currently.
You can create a new folder in you project by clicking the folder with a plus icon.
Double click on the folder you created to navigate inside it.
You can add new assets by clicking the add file button.
Navigate through the file explorer to find the desired asset(s).
After selecting your model asset the Portal will import the model in to use in the editor.