Fitting half-normal distribution to a histogram

How to normalize a histogram and fit a half-normal distribution?

What have you tried? Did you check Documentation?

Distribution parameters estimation:

Estimate the distribution parameters from sample data:

edist = EstimatedDistribution[sample, HalfNormalDistribution[\[Theta]]]

Out[] = HalfNormalDistribution[4.0821]

Compare the density histogram of the sample with the PDF of the estimated distribution:

Show[Histogram[sample, Automatic, "PDF"], Plot[PDF[edist, x], {x, 0, 1}, PlotStyle -> Thick]]