I don't know what model/OS of Android phone you have, but I did find this information in conjunction with the HTC Amaze, and it should be fairly universal:
For Macintosh computers running Mac OS X 10.5 or later, you need AndroidFile Transfer to access and transfer files between your Mac and an Androiddevice running Android 3.0 or later.
To download Android FileTransfer, browse to www.android.com/filetransfer on your Macintosh computer. Click Download Now. When the downloadcompletes, double-click the Android FileTransfer virtual disk on the Mac desktop. In the installer window, drag theAndroid File Transfer character tothe Applications folder icon.
- Plug the small end of the USB cable into the USB/chargingport on your phone.
- Plug the large end of the USB cable into the USB port ofyour computer.
- On your phone, a Choosea connection type message appears.
- Tap Disk drive.
- Tap Done.
- Note: Some applications in use may be stopped or may not be available until you disconnect USB storage.
- On your computer, double-click Android File Transfer to open it the first time (subsequently it opens automatically).
- If prompted, click Open.
- On the desktop, double-click the virtual drive icon labeled No Name (unless you previously changed its name) to access the folders and files on your phone’s memory card.
- Double-click the memory card’s virtual drive icon to access the memory card’s folders and files.
- When you are finished, drag and drop the virtual drive icons into the Trash/Eject.
- Disconnect the USB cord from your computer and then from your phone.
I hope this answers your question,