There are multiple places where you can upload images and other types of attachments which can then be embedded into rich text areas.
These are the insight types that can be assigned attachments. In addition, attachments can be added to comments on tasks and observations.
Press the button or link labeled "Upload attachment". Select the attachments you want to upload by clicking the "Browse" link, or by dragging and dropping the relevant files to the upload area.
Then, click the "Upload x file" button in order to actually trigger the upload. When you are done, you can close the upload widget by clicking the cross in the top, right corner.