You can select either a vector based symbol or raster symbol on the Layer Settings .  This symbol will be used to represent all points on your layer.

Vector Symbols  
These symbols are basic shapes but, unlike raster symbols, they take on all the colors, opacities, and line width defined in your settings above.  Vector symbols can also be color-coded according to the line color or fill color classification rules you have set up in Layer Settings.

Raster Symbols  
Raster symbols are typically more detailed and based on image files like png's or jpg's.  

Click here to upload your own PNG or JPG image to use as a symbol. Any symbols you upload here will appear in the symbol pick list for all maps and all users within your account .  The map will render your symbol at its full pixel dimensions so be sure that you have reduced your image to its desired size before uploading.  For good map aesthetics it is recommended that you keep symbols under 32x32 pixels in size.  16x16 is even better.  

Click here to open the symbol builder screen.  The symbol builder is a way of making simple symbols by choosing a combination of borders, shapes, icons, and sizes. The result is a small image that gets added to your symbol pick list.

Delete Symbols
Any symbols in the list that were Imported, or created by you or other users on your account can be removed from the pick list by right clicking on them.  This will display a deletion confirmation prompt at the bottom of the pick list.

The cancel button simply closes the symbol pick.