Hello Sait,
thanks for your question. It is not easy to go from nairobi, Kenya as the mountain is completely in Tanzania, so you would need either a full day shuttle bus to/from Moshi or aflight to JRO (Kili) airport.
Please see the FAQ about climbing Kilimanjaro for this and much other useful information, it can be found here:
http://7summits.com/kilimanjaro/faq Also check out
http://7summits.com/kilimanjaro/trips.php for affordable expeditions to Kili!
With best regards,
Harry