Visiting Kyoto

Hi,

I will visit Kyoto for 4 days (arriving around 9.a.m and leaving in the evening of 4th day).

What do you suggest me to visit there? I m very confused because there are many places around by train also?
Should I go to Hiroshima and Miyajima as one day trips? or Mount Koya?

Could you please helpe me about what is must to see in Kyoto (must places in center) and around (Mount Koya, Hiroshima and so on?)

Thanks

Start here:

http://www.japan-guide.com/e/e2158.html

http://www.japan-guide.com/e/e3950.html

For Kyoto if you can only visit a few places, then the must-see ones are Kinkakuji, Kiyomizu-dera, and the Fushimi Inari Shrine. None are in central Kyoto but not hard to get to.
Fushimi Inari is the most time consuming to view - you can take a couple of hours to a full day if you want to romp over every trail:

https://www.youtube.com/watch?v=EandKTAwfOM

A night at Koyasan would be an excellent experience. It takes time to get to, but it is well worth it.
Hiroshima/Miyajima are also highly rated. You could do it as a day trip starting very early and only seeing a few places in Hiroshima City (Peace Park/Museum, Shukkeien Garden etc)
and at least ¾ of a day for Miyajima. It might also be good to do it in the middle of your Kyoto visit to avoid a temple burnout.