If you know what these options are, you'll know how to use them. If you don't know – then you will probably not even notice that you changed anything.
So my suggestion would be: Stay with the basic options. When encoding a video, just set a quality level that fits best, and use the highest profile options you want to afford. If you must, choose an average bitrate (or target size).
Don't fiddle around in advanced options unless you've read a book about h.264 and want headaches. No, seriously :)
Now, the options you listed … these are really advanced internal settings of an h.264 codec – you probably don't even want to care about how large the bitrate buffer is. The VBV buffer allows you to sustain peak bitrates for a certain length, but if you're "just encoding a video" for watching on your computer, that doesn't matter either. If you're in a streaming scenario, check the above link for more explanation.
IDR frames are similar to I-frames in MPEG terminology with the difference that frames following an IDR frame can't reference any other frames past this IDR frame. You may want to insert more IDR frames for lossy transmission environments. IDR frames are also used for providing seek points in the video. But since they are significantly larger than normal frames, having more will increase your video size. You probably don't want to change this setting anyway except for when you're encoding for broadcast or Blu-ray (use lower values here).
The motion vector search range influences the way motion detection works. In MPEG video, the encoder will try to exploit the fact that in subsequent frames, you will mostly see the same objects, but at another place. The encoder therefore searches for the original part of a frame and just needs to encode the difference vector. A larger vector search range could reduce the amount of bits per frame, but it's also computationally more intensive. 64 is a sane value for h.264, if I'm not mistaken.
Adaptive quantization steers how many bits will be allocated to certain frames (or, macroblocks actually). This is done automatically – for example, high motion scenes will get a higher quantization factor, and low motion scenes will get a lower quantization factor. This is because the human eye sees errors more easily in low motion scenes. You could change these values to base adaptive quantization on either brightness or contrast, or complexity – but I wouldn't care since the default options are usually good enough and the primary control knob is the Constant Rate Factor value.