What is Bokeh

Bokeh as described by Wikipedia is "the way the lens renders out-of-focus points of light". Different lenses render out of focus objects differently. Getting a lens with a very large aperture (same as very low f value) is essential for good bokeh.

Notice the out-of-focus areas in the following photos. That's bokeh.

I have a 50 mm 1.8 that is the most affordable lens and one of the best lens one can have. This is a must-have lens even for a beginner.

I have another 85 mm 1.4. This lens is excellent. But, be prepared for some manual focusing.

105 mm lenses are also available and some of the costly lenses are awesome ! However, you can get awesome results with the first 2 lenses I mentioned. So, buy this if you have lots of money.

Notice that all the lenses listed above are f/2.0 or less. Also, usually, the higher the mm, the more the bokeh. (As long as the main subject that's being focused is sufficiently close and the background significantly further).

All the lenses listed above are prime-lenses.  This means you can't zoom-in or zoom-out while taking the photo. You will have to move. This is hardly a problem, once you know prime lenses will give you the best results.

<pj>And then there is bookeh</pj>