You can't do this using the task manager itself, but you can use the built-in tasklist command line program to do it. Open a command prompt (cmd.exe) and use the following commands:
Type tasklist to output a list of all the currently running processes
To output as a csv, type tasklist /FO csv
To save the output of the command line to a file, add > filename.csv to the end of the command; for example, tasklist /FO csv > "%userprofile%\desktop\tasks.csv".
For full documentation on the various options for what to output, type tasklist /? into the command prompt.
