about JR west rail pass, Kansai area

I have a plan to traveling in Osaka,Himeji and Nara, I decide to buy JR west rail pass 2000 Y/day.Can I use the rapid train to Nara and special rapid train to Himeji? and can I use JR Osaka loop line instead?

Your pass is valid for all of the trains you have listed.

JR West has two passes - the Kansai area pass, and the Sanyo area pass. (You have the Kansai pass, it's the only 2000 yen option.) This lists the lines you can take:
http://www.westjr.co.jp/english/travel/jrp/index.html

I'll be using Osaka as my base to travel to Nara, Kyoto and Himeji. I plan to buy the 4 day pass. What I'd like to find out is the JR West Pass valid for Osaka to Kansai Airport on the express? Thank you so much.

Yes it is valid on the Haruka Limited Express to Kansai.

Note that the Haruka does not stop at Osaka Station, but ShinOsaka Station (one stop away).