Some regions had this function in 4.4.4 already, but here in Europe it came with Lollipop afaik.

What’s Easy Mode?

Easy Mode is a simplified launcher that gives you just the bare necessities.

It consists of 3 different screens, the green middle screen is the start where you can’t customise a single thing. The blue and orange pages you can add things to. Colour can’t be changed for the 3 screens.

You set it by going to Settings > Personalize > Home screen, and set Easy mode.

If you want back to Blink feed, just go back there and set that instead.