I'm an 11 year-old who has close to zero experience with blender and was recommended to try it by a friend. I had rendered an image without texture and it was very well lit. But, after I textured it in blender cycles it became very dark.
An expanded answer of @cegaton and @PCmath.
In cycles lighting can be one of the most important aspects of a render, it can make a dull image into a full vibrant master piece.
Here's a quick render with only three objects: A floor, Suzanne, and finally a camera. I added no lights to this scene.
Here's the exact same scene with a light, i used the light "Sun".
Without lights the scene can look dull. To add a light press the tab on your bottom left labeled "Add" click expand lights, and select your desired light. Experiment and find out what's best for your scene.