First, the user will need to be added to AllowUsers at the bottom of the file. I'm sure that you've already created myuser and set up a password on the machine you're trying to ssh into.
If it's not there then you'll need to add it at the very end of the file.
Get rid of the "match myuser" and "match all" part and set Password Authentication to yes and Pubkey authentication to no for the time being and then restart the sshd service on the computer you're trying to connect to.
You'll need to first create and then copy the public key over to the folder using the ssh-copy-id command on the computer you're connecting from. Log into the computer from which you are trying to connect as "myuser" and then run the following command:
ssh-keygen -t rsa
It will ask you to enter and confirm a pass phrase for the key and then it will tell you where it has been saved, show the fingerprint, and then the random art image.
The following will copy the public key over to the computer you're trying to connect to. It will prompt you for myuser's password.
ssh-copy-id -i ~/.ssh/id_rsa.pub myuser@host
If you're using a port other than 22, use the following:
ssh-copy-id -p #portnumber -i ~/.ssh/id_rsa.pub myuser@host
After you've done that, you can set Password Authentication to no and Pubkey Authentication to yes on the computer you're trying to connect to and restart the ssh service once again. Try to connect as myuser and it should prompt you for the pass phrase that you created and connect using pubkey authentication.