How do I add a dmg file on casper so I can deploy it on all macs

Judging by your tags, do you want to deploy a package or DMG to a number of Macs? Something like SEP? You use Casper Admin to get the .pkg or .dmg into the Casper Suite, then create a policy to actually deploy it.

Are you new to Casper Suite? Has your organization owned the software for awhile? This is the sort of thing that is normally covered in a JumpStart. If you're new to the suite, but your org isn't, consider the Casper Suite Essentials coursework. The Administrator's Guide is pretty good if you can learn from reading documentation (not everyone can, some need to learn by doing)...

we have had it for a year. I am still playing around with it. I have done flash.dmg before and installed it on all macs. Today I got symantec dmg. I am trying to figure out how to upload it on to casper. I think I know how to deploy it on the macs. Just having a hard time uploading the dmg onto casper to get the 1st step done.

Before you even get to the point of uploading anything, its important to understand the DMG format and how Casper sees them. The DMG format is a bit tricky and can be a little confusing at first. Generally speaking, the Casper Suite treats all DMGs as if they were created with Composer, meaning that it assumes a flat file structure in the DMG that it uses to understand where to copy files to. A typical Composer created DMG will look something like this-

Applications
   Greatapp.app
Users
   username
      Library
         Preferences
            com.company.greatapp.plist

The above would be the structure for a Composer created DMG that contains a single app bundle and a plist associated with the app that would get deployed to either all user accounts or the System User Template if you check the FEU or FUT checkboxes respectively for the uploaded DMG in Casper Admin, or when adding it to a policy.

A vendor supplied DMG is not going to have any of that structure and as such Casper will typically just copy whatever is at the top level of the disk image to the same locations on the target drive, meaning an .app or installer .pkg file will land at the top of Macintosh HD. Not really what you want.

Because of this, you usually have to recreate DMGs from companies using some other method, such as capturing an install in Composer (not the best) or if its drag and drop, copying the app to /Applications, then dragging in to Composer so it captures it in the /Applications/appname.app path and then repackage it up And there are other methods beyond this, but they are dependent on what's in the DMG.

See these 2 feature requests and vote the one up that isn't a dupe if you agree with them:
https://jamfnation.jamfsoftware.com/featureRequest.html?id=707
https://jamfnation.jamfsoftware.com/featureRequest.html?id=881

Generally speaking, application installations are going to take place with a PKG file. Either one you built with Composer or one provided by the vendor if you don't need to customize it.

I had to make a package for deploying SEP 11. I actually have two of them. One for imaging time is just the standard PKG that is built by the SEP console. The other I customized to be able to remove any previous version of SAV or Norton AV, install SEP and start all the services including the ones that run as the user. If you'd like to see what it took for me to get this going I'd be happy to help.