Q: merge events

In iPhoto '11 you merge two events by dragging one event on top of another in Events view. Then you will see this prompt.

What is your iPhoto version? My screenshot is from iPhoto '11.

Another way to merge tow events is to flag the photos in both event. Then use the command from the 2Events" menu:  New event from flagged photos.

iPhoto Menu -> About iPhoto

.

You can also see the version number in the Finder in column view, if you select iPhoto in the Applications folder:

I jusr realized I am not in Iphoto rather I am in Photo.

That makes a big difference, because Photos does not even have events. Events have been replaced by the Moments and Collections.

If you are seeing iPhoto Events - that is a folder with albums.  When Photos creates a new Photos Library from your iPhoto Library, it will create an album for each of your events, and collect these albums in the folder iPhoto Events.  These are regular albums  You can drag photos from one album to another album and then remove them from the source album by selecting them and pressing the delete key.

When you import new photos select them in the "Last Import album" and press the key combination ⌘N to create a new album for them. name the album suitably and drag it to your iPhoto Events folder.

I am not sure how I got out of iPhoto.

During the update to Yosemite MacOS X 10.10.3 the new Photos.app has been installed as part of the system. The Photos.app has been added to the Dock and the iphoto icon removed.  Your iPhoto version will be incompatible with the new system, if you did not update to iPhoto 0.6.1 before the update.If you launched Photos, your iPhoto Library will automatically have been migrated to Photos.

See this help text on the differences caused by the migration:   How Photos handles content and metadata from iPhoto and Aperture - Apple Support

I jusr realized I am not in Iphoto rather I am in Photo.

Then you just be in an album.  If you want to merge Album A into Album B do the following:

1 - open the sidebar with the Option+Command+S key combination.

2 - with the two albums visible in the sidebar click on A.

3 - select all of the photos in A.

4 - drag them onto the Album B icon in the sidebar to add them to B.

5 - verify all of the photos are in B.

6 - delete A from the sidebar.

Also this may help you understand Photos a bit better:

Moments in Photos are the new Events, i.e. groupings of photos sorted by date taken.

When the iPhoto Library was first migrated to Photos there is a folder created in the sidebar titled iPhoto Events and all migrated iPhoto Events (which are now Moments) are represented by an album in that folder. To open the sidebar if it's not already open use the Option+Command+S key combination.

NOTE: It's been reported by several users that if the Event albums are moved out of the iPhoto Library folder in the sidebar they may disappear.  It's not widespread but several users have reported that issue.  Therefore, if you want to assure that you keep those Event albums don't move them outside the iPhoto Events folder.

There's a way to simulate events in Photos.

When new photos are imported into the Photos library go to the Last Import smart album, select all the photos and use the File ➙ New Album menu option or use the key combination Command+N.  Name it as desired.  It will appear just above the iPhoto Events folder where you can drag it into the iPhoto Events folder

 

When you click on the iPhoto Events folder you'll get a simulated iPhoto Events window.

The downside to the simulation is that the Albums/Events can only be sorted automatically by Title. But they can also be sorted manually, either in the sidebar or in the folder's window at the right.  This will change with the release of Photos 2 with El Capitan this fall.  That will allow the sorting by date or title, ascending or descending.

Tell Apple what missing features you'd like restored or new features added in Photos via Apple-Photos Feedback.