Formatting a CSV File

Hi All
Im a bit of a newbie to scripting in powershell so please forgive me if this is a really stupid question;

Im putting together a script to format a csv file that has come out of a payroll system. It has fields that I need to be separated, dates updated into another format, replacing site codes with a name etc. All up I have about 10 changes that need to be done. I have all the individual parts working but to put it all together whats the best way to write the script so it does each step rather than import-csv and export-csv per step. Sorry really noob question

Thanks in advance

You might show what you have already and we could give some suggestions. Otherwise it will be just guessing what you might need.

And please: When you post you code or error messages format it as code. Thanks.