Does $3-4+1$ equal $0$ or $-2$.. or maybe $2$? Does $3 - 4 + 1 = 0$ or $3 - 4 + 1 = -2$?
Makes sense that $(3 - 4) + 1 = 0$ and $3 - (4 + 1) = -2$, but what if there are no parenthesis?
Also, if I have $4$ apples and I add $1$ more apple, then I have $5$ apples, but if I eat $3$ apples, then I have $2$ left.
Any ideas?

Add positives together, and you will have $3+1=4$
The only negative that you have is $-4$
The sum is then $4-4=0$
If you do not have parenthesis you add positives and keep the result.
Then you add negatives and keep the result. Then find the total result by the algebraic sum of those two.
For example $$1-5-3+12-23=?$$
We have $1+12=13$ positives. We also have $-5-3-23=-31$ negatives.
Thus the result is $13-31 = -18$ 
