That means not everyone will have access to it right away but it should be available by the end of the week. The new share feature lets you share albums with people directly through their Google account based on a suggestion from the app.
Whereas before, when you shared an album you had to create a link to it and then share it with people through various means. Such as text, email, or other chat apps.
The new share albums feature in Google Photos adds people to the album directly
Once this change takes place for you, if you share your albums with someone in Google Photos, then they'll be added to that album which will then pop up in their own Google Photos account.
The idea behind this change is to give users more control. But, prior to this new share function it was still possible to add people to albums. They could then open Photos and click on the Sharing tab and see the album that was shared with them.
The main difference now appears to be the ease of use for sharing. Once you hit the share button for a specific album and select someone, a new list pops up with other suggestions so you can add more people. Sharing directly with people's Google accounts is also now going to be the "default" option.
Sharing albums doesn't appear to be much different aside from one other specific thing. Removing people.
Removing people from albums is getting easier
This new update will make it much easier to remove people from a shared album. Currently it doesn't seem like you can really remove someone you've invited to an album unless you turn off link-sharing.
Once you re-enable it you are once again the only person with access to that album. With the new update though, Google states that you'll be able to turn link-sharing on and off like before, but also easily remove people from an album. Presumably without turning link-sharing off.
So again, these small changes may be minor but they're meant to make things easier for the user. Easier to add people to an album directly. And easier to remove someone directly if you ever have a need or desire to.
If you use the app and share albums often enough, keep an eye out for these easier sharing features.