In order to ssh
into a server your identity's public key has to be added to the list of trusted keys. Most commonly this is done per-user:
ssh-copy-id -i ~/.ssh/<identity>.pub <user>@<hostname>
Which can be also done manually:
cat ~/.ssh/<identity>.pub | ssh <user>@<hostname> 'cat >> ~/.ssh/authorized_keys'
After doing that you should be able to log in without need to provide user's password when passing the identity file to the ssh
call.