The difference of course is the symbol between the f and g letters.
The circle [tex]\circ[/tex] notation means we're doing a function composition.
Writing [tex](f \circ g)(x)[/tex] is the same as saying [tex]f(g(x))[/tex] where g is the inner function.
Here's an example
f(x) = x^2
g(x) = 3x
f( g(x) ) = ( g(x) )^2 ... note how x is replaced with g(x)
f( g(x) ) = ( 3x )^2
f( g(x) ) = 9x^2
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On the other hand, the dot notation means we multiply the f(x) and g(x) functions.
Going back to the previous example, we could say
[tex]f(x) = x^2\\\\g(x) = 3x\\\\(f \cdot g)(x) = f(x)*g(x)\\\\(f \cdot g)(x) = x^2*3x\\\\(f \cdot g)(x) = 3x^3\\\\[/tex]
