In this example, the values in column A are "stored as text". This means if you try to SUM column A, you'll get a result of zero.
The VALUE function will try to "coerce" a number stored as text to a true number. In simple cases, it will just work and you'll get a numeric result. If it doesn't work, you'll get a #VALUE error.
Add zero instead
Another common trick is to simply add zero to the text value with a formula like this:
This forces Excel to try and convert the text value to a number to handle the math operation. This has the same functionality as VALUE above. In the example shown, C7 uses this formula.
Stripping other characters
If a cell contains non-numeric characters like dashes, punctuation, and so on, you'll need to remove those characters before you can convert to numbers.
The formulas in C8 and C9 show how to use the LEFT and RIGHT functions to strip non-numeric characters from a text value before it's converted to a number. You can also use the MID function in more complicated situations. If you need to strip extra spaces or other non-printing characters, see the TRIM and CLEAN functions.
Finally, the SUBSTITUTE function will let you remove characters with "search and replace" type functionality.