There are a lot of ways to create a wood grain effect. You can by rollers with a bold pattern on them for applying or thinning applied paint. Another approach is to use a brush to apply paint in specific directions and in multiple layers.
Using a manufactured door as a grain guide, above, I started painting our cellar door last week by applying a coat of Killz using a directional pattern.
Later last week, I added the first color coat, repeating the pattern. The white Killz shows through at this point, exaggerating the effect. But it will still have a strong grain pattern after the second coat of paint is applied and to the casual eye, will look like the door is textured instead of flat and featureless.
For the record, my wife really hates this look. So, for the next coat, I elected to use a roller to put a smoother texture on. Happily, some of the "grain" still shows through but the top coat is smooth and glossy. This is what I ultimately wanted - a finished but deep look. I'll post about the final result when the trim is stained and installed. Should have the hardware on then too.
I had wanted to do my wood staining and painting this way since I took notice of Chinese and Japanese antique furniture. They apparently, in bygone golden years, would use 13 or so layers of lacquer to create just the right depth and luster. I'm happy to use three modern multipurpose products to create just a touch of depth. :-)