You can access the Add Photos tool from the Event Dashboard of the event you would like to add photos for.
In the first section you can drag and drop photos of the event. A preview of the photos will show at the bottom of the section. From this preview you will be able add bib numbers (if you would like to tag racers) and also create a caption for each photo (also optional).
If you would like to copyright your photos you can add an optional watermark in the second section to keep participants from downloading a picture directly from the event page.
In the third section you can add a link if you would like to redirect your participants to photos that are for sale from the event.
Once you have completed the sections you need select the button in the top right, Publish Photos. This will automatically notify everyone that took part that photos have been uploaded of the event and gives them a link to view the pictures.