A lot of times computers play a position very differently from humans, and this can throw off the score estimations by a lot.
when me and my computer don't connect
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If a computer sees a good line, even if it hasn't been played yet, it gives an advantage. If you don't see that line you may not have any advantage at all. I remember one game I analyzed with Fritz, it said my opponent had a huge advantage at one point when the game was actually turning my way. Neither of us saw that he could have won my rook three or four moves from that position.
Well first of all make sure you're giving it a good amount of time to "think" -- if you let it run for 20 seconds it's not done "looking" at the position yet. Sometimes a +0.80 +/- will drop to a +0.25 = (not often that large of a drop but it changes all the time).
Often times I'm not sure why an evaluation is given actually. In those cases I play it out vs the computer, I try to "prove" why I think it's supposed to be equal and Rybka shows me why exactly those moves end up in a +1.23 (or whatever it's reading). And if Rybka plays an odd move then take it back and substitute a move you were thinking of. Is there still an advantage, or does the advantage lie in a specific sequence of moves?
Often if it's a big number and you're not sure it's something tactical you can't see. If it's very small like .30 or .40 then take it with a grain of salt, it may still be equal (Rybka even draws itself after claiming such advantages). When it says +.60 or +.80 or something to where it's not winning material but there's definitely an advantage, again just play it out.
Often I play out positions even if I agree with the evaluation. When my move makes the evaluation go down, I try to figure out why by continuing to play. Eventually you see what's wrong with your move or idea, then backup and try again etc. Again taking small drops in evaluation with a grain of salt, many times Rybka wont agree at first but a few moves down the line it "changes it's mind" and you're move is just as good. Of course other times it just goes from bad to worse and you have to admit you were wrong 
This and playing blitz are about the only things I did with chess for about the first 3 years I started playing.
I need some help with analysis you know how after a chess engine has looked some move's ahead of a position and it shows which side if any has the advantage well normally I'm able to tell what the advantage is wheather it's pawn structure or somethin else like material etc.. but what should I do when my engine arrive's at a variation giving the positon advantage to one side but I don't see how that side has an advantage (For example say Rybka says white has the advantage in a position but you can't tell how what do you usualy do.