Kdenlive is able to create simple titles as described here. We can also work with external image editors (like GIMP) to create more sophisticated titles and then add them to the project list as video clips.
To create a title clip, select "Add clip" icon () and, in the context menu, select "Create Text Clip". A new window like this will be presented:
In this window, you can give a name to your clip, define the duration, the letter type, size and colour. You'll also have the following icons:
You can now select the "Enter text" icon, write the title and click "OK". The text will appear in the window and you can drag and drop it wherever you want on the screen. To improve your title, click the "Draw box" icon and, with the left mouse button pressed, draw a box on the screen. Before doing so, you need to change the box colour in the same way as you did for the text. If the box and the text have the same colour, they may interfere!
Don't worry if you can't see your text now! Select the box and try with the "Bring to front/send back" icons. Better now, huh?
By dragging and dropping the box and the text and by playing with the movement icons, you can obtain quite nice titles!