Did you learn how?
Well, here's a quick lesson.
Make a new layer.
Use the pen tool to draw a path along the road/river/etc. by clicking on the start point, major turns, and the end point. As you click, drag the pen in the direction you want to go.
Using the arrow tool, use the handles on the points you made to fine tune the bends in the curve.
Choose the type tool. Choose your font, color, size, spacing, and set the justification in the Paragraph window to Left Justified.
Click on the beginning of your path and type your text in. You may have to zoom out to see the cursor.
You can use the arrow tool again to move the points and manipulate the curve handles.
If the type disappears part way, try pulling it back with the arrow tool.
If you type and the text starts at the middle of the path, you probably have the text center justified. That's why it's always good to check that it's left justified before you start to type.