Ciao,
ti posto parte del manualetto di Gimp, sperando che possa esserti utile:


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To insert text in a Gimp image, click on the Text tool in the toolbox and
then click at a spot inside the image. The Text Tool dialog box will open
and display a list of the installed fonts. Type in the text you want in the text
box in the bottom of the dialog. Click on the font you want, set the parameters if
you want to change the default values and click OK.
Now your text string will appear as a floating selection in your image. The text
will have the same color as the foreground color in the toolbox. If for some reason
you aren’t happy with the text — if it’s too small, too large or if the font just
doesn’t look right — you can delete the floating text selection by pressing the
cross (Delete Layer) button in the Layers & Channel dialog.