The LEFT function can be used to find the start of a text string if we know how many characters we wish to take. It takes the form "=LEFT("TextString", 4)", where 4 is the number of characters you extract. So the above formula would return "Text". If we changed the 4 to a 1, it would return "T". Often the text string will refer to the text in a certain cell. When referring to a specific cell or range, it is not necessary to use quotation marks.
The RIGHT function takes the end of the string but follows the same principle. If "TextString" were written in cell A1, we would use "=RIGHT(A1, 6)" to return "String".
The MID function is a little more complex in that we have to specify the position of the first character we wish to extract, as well as the number of characters we wish to extract. So "=MID(A1, 5, 3)" would, in the above example, return "Str". "S" is that 5th character and we have said we want to take 3 characters in total. Note that if we ask for more characters than remain in the string e.g. "=MID(A1, 5, 10)", it simply returns the remainder of the text. In this case, it would return "String".
These three functions all require numerical inputs. This is fine for manipulating a column of identical length text strings such as state/zip codes e.g. "NY 10001", "CA 99999". To manipulate more complex text strings requires the FIND function.