The weekday field contains a number where 0 represents Sunday. There is no support for human-readable weekdays in any crontab variant I have come across.
If you want this to execute every month, just put * for the month.
0 1 * * 0 /home/myusername/dir/cp.sh
As long as the script is executable (chmod +x cp.sh) and has a valid shebang (#!/bin/bash as the very first line of the file) you don't need to explicitly tell the OS to run it with bash, just like on the command line.
crontab runs your jobs from your home directory so you could replace /home/myusername with . if this is running from myusername's account. If $HOME/dir is in your PATH you only need cp.sh (but take care to set the PATH where cron, too, can see it!)
Any output or error messages will be sent by email if your server is set up to handle that. This is slightly obscure and sometimes bewildering, especially if you don't actually have email properly configured, so many users add a redirection to a log file for every cron job.
0 1 * * 0 cp.sh >>cp.sh.log 2>&1
(Some beginners like to redirect everything to /dev/null and then come here to ask us what's wrong when there's an error. Of course, we don't know, either.)
The Stack Overflow crontab tag info page has syntax advice, troubleshooting tips, and a link to a site where you can generate a valid crontab from a newbie-friendly form where you just click buttons and move sliders to say when your job should run.
