Variables in Database Control Pro Command Sequences have the same purpose as variables in all programming languages - To store data which varies.
Command Sequences are a list of Commands, every Command has different properties providing different proccesses and results. Many of these Commands are based on variables.
All a variable is, is a name and a value. The name doesn't change, but the value does.
You might need to use a variable to provide a Command with information. For example, if you want to write data to the database, you will need to provide the data which needs to be written to the SetData Command. Sometimes this might be the same data every time such as 'Hello World', but in other cases it might change such as when writing a username to the database as it could be 'John' or 'Mark' or some other name. If the data changes you will want to use a variable.
You might need to use a variable to store information created by a Command. For example, if you want to read data from the database, you will use the GetData Command which will return the data. You need a way to store the data which is by using a variable.
When using variables in Command Sequences, you will have to type the variable's name into the correct field of the property of the Command. The value of every variable is in string format. If you are using a variable as a float or int, (unlike normal programming) you can ignore the types as all strings will be parsed into the type required.