how to upload photos that are already in Photos to iCloud?

Good afternoon yjlee,

Welcome to the Apple Support Communities!

It sounds like you are trying to set up iCloud on your Mac, and we'd like to help.

It appears you have reviewed the Set up and use iCloud Photos article before coming here.

Did you follow the section "Turn on iCloud Photos" for your Mac?

"On your Mac

1. Choose Apple menu  > System Preferences.
2. Click Apple ID. 
3. Click iCloud in the sidebar, then select Photos. 

If you have an earlier version of macOS, go to System Preferences > iCloud. Click Options next to Photos, then select iCloud Photos."

Another section of the article explains the upload process:

"When you turn on iCloud Photos, the time it takes for your photos and videos to upload to iCloud depends on the size of your collection and your internet speed. If you have a large collection of photos and videos, your upload might take more time than usual. You can see the status of the upload.

On your Mac, open the Photos app. Select Library in the sidebar, then click All Photos in the list of tabs in the toolbar. Scroll to the bottom of your photos to see the status of the upload."

If the issue persists, you may need to reach out to Apple for help with this:

Contact Apple for support and service

Take care.

Hi yjlee,

Happy to hear your iCloud Photos are synced now.

Please be sure to review the Set up and use iCloud Photos article carefully, as it contains a lot of valuable information.

Remember that iCloud is mainly a syncing service. You can export your valuable memories to have another copy of them on an external drive.

Archive or make copies of the information you store in iCloud

Export photos, videos, slideshows, and memories from Photos on Mac - Photos User Guide

Enjoy the rest of your day!