DK,

I am gonna try to help you.   I have uploaded 2 images of my computer program Shredder doing the analysis so this way you can better see what I am talking about.

There is one image where the chess pieces are on the starting position.   Let's start with that.  The analysis window is on the right side.  We see  1.  d4b6 +0.43, just below that it says 1...Nf6 +0.01, so what that means is that the computer thinks that a black response of Nf6 on the first move instead of b6 maybe better for black by about 0.4 (now please remember, at this very early stage, these numbers are somewhat subjective, there are different good answers to d4, but let's not worry about that, I am just trying to teach you how to interpret the computer output).

Now your second move d5 gets a score of -0.09, just below d5, it says 2.e4  +0.49, so here the computer thinks that e4 is a better move than what you made by about 0.58 pawns and I would say your second move was probably therefore a little inaccurate.  

Now let's go to the second picture where the final position is shown.   Again on the analysis board, move 5. Bg5 -0.34 whereas below it is the computer suggested 5. dxe6 +0.06, so here the computer thinks that your 5th move was inaccurate by around 0.4 pawns (which is to be honest with you not that much and my human interpretation is that your 5th move was probably ok).   Then the rest of your game moves follows and as you can see computer's analysis did not find any fault with either side, black or white for the rest of the game. 

This is from Shredder, as I said you can download it for a month for free, no obligations and if you like it, then you can purchase it.   So you can get the same thing and do the same thing.    Otherwise, as I told you before, you can go move by move in Tarrasch GUI and whenever you see a big change in the evaluation, that's when you can tell a wrong move was made and you can see what the computer's suggested move is.

On Tarrasch, you ask what does a long line mean?   The long line is what computer believes is the best move, best reply to that move, best reply to the reply, etc, etc.   In other words, the long line is the computer generated "variation" of what would be the best moves to follow, if a certain move is initially chosen.   If you change that move, then you'll get a different long line, a "different variation".   That gives you a chance to play through different possible moves in one position, that's called "analysis".  

Good luck.

Sure

DK,  let me give you one final example, it's an extreme one but it will help you more understand the engine's output.   In the picture you have the final position of the Scholar's mate.  On move 3 for black, b6, computer indicates +M1, that means that the black move led to a mate in one position in favor of white.   Below it computer says 3...g6 -0.53 meaning that black should have played g6 resulting in a position with a slight advantage for black.