You can upload your documents under individual protocol step or results tab within a task. A task is a subunit of an experiment and experiment is a component of the project, so everything that you upload within a task is part of the experiment and project.
In the first case, you need to open a task to enter its overview, which is Protocol steps overview. Then click on the Edit step icon, select the File tab and click Add file. Choose a file from your computer and click Save. For easier understanding see the GIF below.
The second option is to upload files under the results section. After you open a task, click on the RESULTS tab. Among three green buttons, which are representing three different types of results, select the File button. Click the Browse to add button, choose a file from your computer and write the file name in the blank field. Click on the Add file result to finish the action. For easier understanding see the GIF below.