Q: how to transfer media from iPhoto library to iCloud?

Hi stefiesan,

I understand that you want to upload pictures to iCloud and use the iCloud Photo Library. I can help you out with that. 

Now you can upload photos, you can use iCloud.com. You can do this by following the steps outlined below. 
 

Add new photos and videos

1. Go to Photos on iCloud.com.

2. Click Upload, then select the photos and videos you want to add.

    

   Note: Photos must be in JPEG format to be uploaded via the Photos web app.

3. Click Choose to upload them to iCloud Photo Library.

 

Access your photos and videos on iCloud.com
http://help.apple.com/icloud/#/mmc50669030d

Now to have a more seamless process, you might want to consider updating to OS X El Capitan if you can. This will give you the Photos app that will show you your photos that you have uploaded and will be able to be seen on all devices. The steps to update are outlined in the article below. 

Upgrade to OS X El Capitan
https://support.apple.com/en-us/HT201475​ 

Have a good day.