How to make background blur?

I have Nikon D5200 with Tamron AF 18-200mm (IF) Macro F/3.5 - 6.3
How to make background defocused in portrait?

For clarity, "blur" is caused by camera or subject movement when using a shutter speed that is too long to prevent blur

Out of focus can include selective depth of field.

Here is what is necessary to assure out of focus backgrounds

* use a long lens (your 18-200 mm at 200 mm
* shoot with the photo with the lens aperture wide open (f/6.3 in the case of your lens)
* place the subject as close to the camera as it will focus
* make sure that the background is at least 30 feet behind the subject.

The 18-200 mm lens is really NOT the best lens for shooting portraits. The best lens for that use using your D5200 is either the Nikkor 50 mm f/1.8 or Nikkor 85 mm f/1.8

Position subject as far as possible from the background. Position camera as close as possible to the subject. Zoom in past 50mm. Set to lowest f/number allowable. Shoot.

Use a focal length of at least 50mm - longer will produce more blur
Use an aperture of of at least f/4 - larger aperture (smaller number) will produce more blur
Be around 10' from your subject - Closer will produce more blur
Keep the subject away from the background - Further away will produce more blur.

Each of these points on their own will have an affect on how much blur you'll be able to produce. Use them together for the greatest amount of blur. I say "more blur," which is another way of saying that it produces a shallower depth of field.