There are a few standard data types in programming:
Character (char) - a single letter, number of symbol eg: a, 1 , $
Strings - this is a string of characters - used for Text. It includes letters, puctuation and numbers but you can not do maths with the numbers as the computer sees them as text. eg "Fish3!" It is technically a compound data type.
Int or integer - whole numbers, can be positive or negative eg 99
Float, also called Real - floating decimal point. Any number with a decimal part eg 4.25
Boolean (bool) can only take 2 values, usually TRUE or FALSE, but could be 1 and 0, Yes /No
Each data type needs a different amount of memory to be stored so using the correct one makes your programs more efficient.
To switch a variable from one data type to another you Cast it. The GCSE Computer Science exam sometimes has the question "What is casting?" in it so its worth remembering this.