Once you have become familiar enough with the look and feel of a true sentence to
eliminate fragments from your writing, you will be able to eliminate run-ons fairly
easily. A "run-on" is, simply, two sentences joined in the punctuation of a single
sentence.
Parents just don't understand well if they do they don't act like it.
Either there is no punctuation at all between the two thoughts—where there needs to be a period or a semicolon—or there is only a comma. Run-ons of the second variety are called comma splices.
Our father was a madman in his youth, he would do anything on a dare.
Run-ons can be corrected very simply.
1. Use a period and a capital letter to break the two complete thoughts into separate sentences:
My grades are very good this semester. My social life rates only a C.
2. Use a comma plus a coordinating conjunction (for, and, nor, but, or, yet, so … also known as “FANBOYS”) to connect the two complete thoughts:
My grades are very good this semester, but my social life rates only a C.
3. Use a semicolon (but sparingly—semicolons draw attention to themselves) to connect the two complete thoughts.
My grades are very good this semester; my social life rates only a C.