There are two ways of adding a dataset to your account. The first one is to upload yourself the images. The second way is to clone an already existing dataset to your account.
You can click on the top-right + icon of the Datasets tab to create a new dataset. From there you can upload the pictures, set a name and description for your dataset and choose if it will be public or private.
In the dataset tab you can browse public datasets then select one to clone it on your account.
You can either clone only images or chose to clone also annotations
From this page you can:
Add new images to your existing dataset with the top-left + icon
Rename the dataset
Delete the dataset with the gears-drop down menu