When functions is determined by different formulas on different intervals then function is piecewise.
For example, f(x)={1−xifx<0x2ifx≥0 is piecewise because on interval (−∞,0) f(x)=1−x and on interval [0,∞) f(x)=x2. 
Now find f(−2), f(1), f(0) and draw graph of this function.
Remember that function is a rule. In this case it tells us that if x<0 then apply f(x)=1−x, otherwise apply f(x)=x2.
Since −2<0 then we apply f(x)=1−x: f(−2)=1−(−2)=3.
Since 1>0 then we apply f(x)=x2: f(1)=12=1.
Since 0≥0 then we apply f(x)=x2: f(0)=02=0.
Now, to draw this function we draw graph of the function f(x)=1−x on interval (−∞,0) and graph of the function f(x)=x2 on interval [0,∞).
Note, that open dot indicates that it doesn't belong to the graph. Indeed, f(0)=0, so point (0,0) is on the graph, but (0,1) is not.