String variables are variables that hold zero or more characters such as letters, numbers, spaces, commas and many more. You can't use numeric functions such as addition or subtraction on string variables. You can, however, extract one or more characters (a substring) from them, glue them together (concatenate) and a couple of other functions.
Like so, working with string variables in SPSS is super easy: you just need to know and combine the right building blocks. These are explained and demonstrated in the tutorials listed below. Enjoy!