sorry if this question will be silly for you For example one site adds a link to my site (backlink for me) His main page has PR4 other pages has PR2 (the same site, just other pages) If he adds my link to his main page, I have backlink PR4? But for example he adds to five pages, main page and 4 other pages so I have 1 backlink from PR4 and 4 backlinks from PR2? explain, please
That is correct. You want links from sites that are same topic and have decent Pr. The main page link is best but the Pr 2 pages are ok for some extra links. You get a back link for each page your sites url is on. Just do not trade links or get links that use redirections. No follow links do not help site either.
OK, one more question if I check how many backlinks I have with backlinkwatch.com and count every PR5s PR4s PR2s and so on, is it possible to count what's my PR should be?
That is not true. Just because a link is no-follow does not mean it is unhelpful. It just means it doesn't pass PR. I'll take 100 no-follow links over a handful of links that pass PR anyday.
There have been countless studies that no-follow is ignored by the SERPS they want you to believe that its important but the reality is, Google, MSN and Yahoo don't care.. I've built sites that only had no-follow links and had a very good pr of about 6. I'll scrounge up some articles about this..
you can see your pr by checking here: http://www.prfind.info/ and dont forget that backlinkwatch show you about 2 weeks in the past.
all the links from that web site will help you to get better seo results but pr 4 home links will help you more and the subpages will help you less than the home page