Lets say you have 3 CSV files, called 1.csv, 2.csv and 3.csv
All you need to do is decide which CSV you want as the 'master' file (1.csv) then delete the header row from the rest. Then simply do the following:
In Linux, Unix or OSX
cat 2.csv >> 1.csv cat 3.csv >> 1.csv
In MSDOS, Windows or any other variant
type 2.csv >> 1.csv type 3.csv >> 1.csv
>> on a command line means "Append to"
cat / type is simply a command to display the file
So cat 2.csv >> 1.csv is saying read 2.csv and append it to 1.csv.