Input: 4+5$

Step  Stack  Input  Action
1     $(0)   4+5$

Start off in state 0, look at the y.output.
If you see a NUMBER in the input, you have to shift state 3 onto the stack.

Step  Stack    Input Action
1     $(0)     4+5$  Shift
2     $(0)4(3) +5$ 

Now look at the state on top of the stack, it's 3. Look at y.output for state
3. It says expr : NUMBER_ The _ means that's where you are, you've
read NUMBER. You can reduce it to expr.

Step Stack    Input Action
1    $(0)     4+5$  Shift 
2    $(0)4(3) +5$   Reduce using expr -> NUMBER 
3    $(0)expr +5$ 

Now look at the last state on the stack, 0. Look at y.output for state 0. 
It says expr goto 2. So you push 2 onto the stack

Step  Stack       Input  Action
1     $(0)        4+5$   Shift
2     $(0)4(3)    +5$    Reduce using expr -> NUMBER
3     $(0)expr(2) +5$

Now look at the state on top of the stack, it is 2. Look at y.output for state 2. It says + shift 5.

Step  Stack           Input  Action
1     $(0)            4+5$   Shift
2     $(0)4(3)        +5$    Reduce using expr -> NUMBER
3     $(0)expr(2)     +5$    Shift
4     $(0)expr(2)+(5) 5$

Now look at the state on top of the stack. It is 5. Look at y.output for state 5. It says NUMBER shift 3.
Step  Stack               Input  Action
1     $(0)                4+5$   Shift
2     $(0)4(3)            +5$    Reduce using expr -> NUMBER
3     $(0)expr(2)         +5$    Shift
4     $(0)expr(2)+(5)     5$     Shift
5     $(0)expr(2)+(5)5(3) $

Now look at the state on top of the stack, it is 3. Look at y.output for state 3. It says expr : NUMBER_. You can reduce 5 to expr.

Step  Stack               Input  Action
1     $(0)                4+5$   Shift
2     $(0)4(3)            +5$    Reduce using expr -> NUMBER
3     $(0)expr(2)         +5$    Shift
4     $(0)expr(2)+(5)     5$     Shift
5     $(0)expr(2)+(5)5(3) $      Reduce expr -> NUMBER
6     $(0)expr(2)+(5)expr $

Now look at the state on top of the stack. It is 5. Look at y.output for 5. It says expr goto 10.

Step  Stack                   Input  Action
1     $(0)                    4+5$   Shift
2     $(0)4(3)                +5$    Reduce using expr -> NUMBER
3     $(0)expr(2)             +5$    Shift
4     $(0)expr(2)+(5)         5$     Shift
5     $(0)expr(2)+(5)5(3)     $      Reduce expr -> NUMBER
6     $(0)expr(2)+(5)expr(10) $

Now look at the state on top of the stack, it is 10. Look at y.output for state 10. It says expr : expr+expr_ So you can reduce.

Step  Stack                   Input  Action
1     $(0)                    4+5$   Shift
2     $(0)4(3)                +5$    Reduce using expr -> NUMBER
3     $(0)expr(2)             +5$    Shift
4     $(0)expr(2)+(5)         5$     Shift
5     $(0)expr(2)+(5)5(3)     $      Reduce using expr -> NUMBER
6     $(0)expr(2)+(5)expr(10) $      Reduce using expr -> expr+expr 
7     $(0)expr                $

Now look at the last state on the stack. It is 0. Look at y.output for state 0. It says expr goto 2.

Step  Stack                   Input  Action
1     $(0)                    4+5$   Shift
2     $(0)4(3)                +5$    Reduce using expr -> NUMBER
3     $(0)expr(2)             +5$    Shift
4     $(0)expr(2)+(5)         5$     Shift
5     $(0)expr(2)+(5)5(3)     $      Reduce using expr -> NUMBER
6     $(0)expr(2)+(5)expr(10) $      Reduce using expr -> expr+expr 
7     $(0)expr(2)             $

Now look at the state on top of the stack. It is 2. Look at y.output for state 2. It says Line : expr_. So you can reduce

Step  Stack                   Input  Action
1     $(0)                    4+5$   Shift
2     $(0)4(3)                +5$    Reduce using expr -> NUMBER
3     $(0)expr(2)             +5$    Shift
4     $(0)expr(2)+(5)         5$     Shift
5     $(0)expr(2)+(5)5(3)     $      Reduce using expr -> NUMBER
6     $(0)expr(2)+(5)expr(10) $      Reduce using expr -> expr+expr 
7     $(0)expr(2)             $      Reduce using Line -> expr
8     $(0)Line                $

Now look at the state on top of the stack. It is 0. Look at y.output for 0. It says Line goto 1.

Step  Stack                   Input  Action
1     $(0)                    4+5$   Shift
2     $(0)4(3)                +5$    Reduce using expr -> NUMBER
3     $(0)expr(2)             +5$    Shift
4     $(0)expr(2)+(5)         5$     Shift
5     $(0)expr(2)+(5)5(3)     $      Reduce using expr -> NUMBER
6     $(0)expr(2)+(5)expr(10) $      Reduce using expr -> expr+expr 
7     $(0)expr(2)             $      Reduce using Line -> expr
8     $(0)Line(1)             $

Now look at the state on top of the stack, it is 1. Look at y.output for state 1. It says $end accept.

Step  Stack                   Input  Action
1     $(0)                    4+5$   Shift
2     $(0)4(3)                +5$    Reduce using expr -> NUMBER
3     $(0)expr(2)             +5$    Shift
4     $(0)expr(2)+(5)         5$     Shift
5     $(0)expr(2)+(5)5(3)     $      Reduce using expr -> NUMBER
6     $(0)expr(2)+(5)expr(10) $      Reduce using expr -> expr+expr 
7     $(0)expr(2)             $      Reduce using Line -> expr
8     $(0)Line                $      Accept

Hope that helps!