Importing Data

SetDirectory[NotebookDirectory[]];
data=Import["Test","Table"][[1]]
Fourier[data,
FourierParameters->{1,-1}
]

What is a DFT

Manipulate[
f[x_]= a0 + a1 Cos[x] + a2 Cos[2x] + a3 Cos[3x]+b1 Sin[x] + b2 Sin[2 x] + b3 Sin[3 x];
Data = Table[f[x],{x, π/24, 2 π ,π/24}];
FData=Fourier[Data,
FourierParameters->{1,-1}];
GraphicsArray[
{
ListPlot[Data,
PlotRange->{-7,7}],
ListPlot[{Re[FData],Im[FData]},
PlotRange->All],
ListPlot[{Re[FData],Im[FData]},
PlotRange->{{0,10},All}
]
}],
{a0,-1,1,0.1},
{a1,-1,1,0.1},
{b1,-1,1,0.1},
{a2,-1,1,0.1},
{b2,-1,1,0.1},
{a3,-1,1,0.1},
{b3,-1,1,0.1}
]