Understanding forward process in diffusion models

I was reading a blog on diffusion models where I came across this expression. I didn't understand why it is \begin{align} \sqrt[]{1-\beta \small{t}}*\large{x}\small{t-1} \end{align}

and what exactly the term variance schedule \begin{align} {\beta \small{t} \space \large\epsilon (0,1) } t = 1 \space to \space T \end{align} signifies

Blog link