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Photos - Yes.
Videos - that depends up on the type/format of videos.
Where are the photos and videos saved ? Are they in Photos app ?
Then you can sync them to your iPhone. Connect the iPhone to your Mac and open iTunes. iTunes will recognize your iPhone. In case, If asked to setup as new iPhone or restore from backup, select setup it as new iPhone.
Then click your iPhone icon at top left next to Music, Movies etc icons.
This will bring Summary page of iPhone. Then click Photos option in left column. Enable "Sync Photos" option. Select the source (iPhoto Library). Click Apply or Sync button. That's it.
This will download all the photos and videos from iPhoto to iPhone. You can also select the albums to transfer instead of syncing the entire library.
Note : If you are using a very older version of OS X, then iTunes will not recognize your iPhone. So let me know if iTunes app doesn't recognize your iPhone, so we can update your Mac.
Please let me know if that didn't work, so I will continue to help you