All errors have an error message which starts with an exclamation point.
See the LaTeX manual or LaTeX Companion for explanation. The error message is printed on the next line, which starts with a number and then the text of the line that caused the error. The part of the number after the decimal point is the line number where the error occurred. If you cannot figure out what the problem is by looking at the error message, you can go to the offending line in the original document and look at it. The error message should make more sense after you have looked at the offending text.