In what software?
how do I do to make labeled curved text like for example following the line of a river or else?
While you can do it in Photoshop/GIMP, its far easier to do that in vector applications like Illustrator, Inkscape, or Xara Photo & Graphic Designer. In fact there are many GIMP only or Photoshop only cartographers that prefer to do labeling (especially text on a curve operations) in vector. So once the art design part of the map is done. You import that into your vector application of choice to do the labeling.
In most vector apps, you draw a short curved line, making sure that line is long enough to include the entire typed word. Then type your word name in the size and your font choice. Select both the typed text and the drawn line, and click "text to curve", then the typed words jump to the top edge of the drawn line. Sometimes when you're done you need to delete the line (depends on which app you're using.) That's it.
I have inkscape and photoshop , any tips on those?
In photoshop the easiest way would be to use the freeform pen tool if you use a graphics tablet.
Just draw the curve along the river as you like.
Then select the type tool and click on the curve path you just created.
If you aren't happy with the curve path you can left click the type layer and the go to edit>transform path>distort and play around with reshaping it.
It won't appear that the text has changed until you accept the transform operation.
You can get a lot of variation that way.