Answer
\begin{align*}
\text{Center: }&
(1,1)
\\\text{Radius: }&
2\text{ units}
\end{align*}
Work Step by Step
The Center-Radius Form of the equation of circles which is given by $
(x-h)^2+(y-k)^2=r^2
$ has center at $(h,k)$ and radius equal to $r.$
In the center-radius form, the given equation, $
(x-1)^2+(y-1)^2=4
,$ is equivalent to
\begin{align*}\require{cancel}
&
(x-1)^2+(y-1)^2=2^2
.\end{align*}
Hence, the given equation has the following properties:
\begin{align*}
\text{Center: }&
(1,1)
\\\text{Radius: }&
2\text{ units}
.\end{align*}