Can someone tell me what the radian value is for this number and how they got it?

Thanks

On a graph plot the point A(2,1)
Let C(2,0) be the point on the x-axis

x is the angle AOB and tan x = 1/2

Since angle x is not one of the special angles, you will have to use a calculator to find it (or trig tables from an old math textbook)

set your calculator to Radians,
enter "2nd" "tan" .5
or "shift" "tan" .5 depending on your calculator.

you should get appr. 0.4636
or 26.565º