Sytist is a very robust system with a lot of features. It can be used as an entire website or just an addition to your website for selling photos.
For just selling photos, here is how you want to set it up.
1) Site Content -> Create New Section. In the new section wizard select Client Galleries and create that section. Then to add a new gallery, just click add new page to that section you created.
2) Go to Site Content -> Mange Home Page. Click Featured Content and select the section you created for your client photos. This will display the galleries on your Sytist home page.
You can also click the more options link, scroll down and check the option to add the find my photos form on the home page so clients can enter their gallery password if needed.