I have experience with drawing with color pencils, water colors and pastel. Now I want to try it with markers. As I am a newbie to markers, I have a lack of knowledge about those. I wonder if it is hard to blend colors when using markers?
It is possible to blend using markers, though like any new medium it can take some practice as well as depend on the type of marker you're using.
Blending water-based markers requires little to no additional special equipment, just some water and a way to apply it. As you mention experience with watercolors, this may feel fairly intuitive to you. You'll use either a standard brush or a water brush (a hollow brush pen that can be filled with water) to apply water to your paper and fade or blend your colors. Additionally, you can use a non-porous surface to build up some ink from the marker and use it very similarly to paint by picking the ink back up off that surface with your brush/water brush.
The blog The Frugal Crafter has an entry showing a wide variety of samples of both test blending and artwork done using inexpensive water-based markers and brushes to blend.
Brands include Tombow, Marvy LePlume, Crayola, Mr. Sketch, etc.
With alcohol based markers, the key to blending is to work while the ink is still wet; this can mean working quickly from one color to another on the page, touching the tips of two markers together, or applying one marker to a nonporous surface and picking the color up with another. Additionally, many brands feature a "colorless blender" pen that contains only the solvent and can be used to help fade a color into the paper's color.
User Khallandra on DeviantArt offers a nice rundown of various blending techniques with a large number of sample images.
Brands include Copic, Prismacolor, etc.
Solvent-based (xylene, etc) markers may behave fairly similarly to alcohol-based markers, and even may include the option of a colorless blender for them. Their blending is not as smooth as that of alcohol-based markers, however this may vary to some degree by brand. I'll note that while I personally have used them in the past, it was briefly and some time ago due to the heavy fumes released by the solvents, which can cause eye and lung irritation.
The Curiously Creative blog has a guide to general marker types, which has the best general, neutral information I could find on solvent-based markers.
Brands include Sharpie, Chartpak, etc.