The backslash character (\) turns off the special meaning of the character that follows it. For example:

echo it\'s me

prints:

it's me

If you just try:

echo it's me

without the backslash, the shell prints a > prompt after you press <Enter>instead of the usual $. The > prompt is a continuation prompt. An apostrophe ' without a backslash is taken to be the start of a string and the shell assumes that the string keeps going until you type another apostrophe, even if that goes on for several lines. The shell does not process the string until you type the closing apostrophe.