writerow
expects an iterable, each element of which will be written to the file, separated by the delimiter. Hence when you give it a string (which itself is an iterable), it writes each character to the file, separated by the delimiter.
What you want to do instead, is to supply the "row" as a list of strings. In your case, each row has only one string, so supply each row as a list with only one string.
The CSV format requires a delimiter of some sort. Classically, this delimiter is the comma - hence the name (CSV = Comma Separated Values). However, should you feel the need to use a different delimiter, you could of course do so (typical choices include space, tab, hyphens, etc)
import csv
export=open('./images2/test.tfw', "wb")
writer=csv.writer(export, delimiter=',', quoting=csv.QUOTE_NONE)
writer.writerow(['0.06'])
writer.writerow(['0.00'])
writer.writerow(['0.00'])
writer.writerow(['-0.06'])
writer.writerow(['-10.59'])
writer.writerow(['38.49'])
export.close()