Problem Creating Commit Messages

Hello, I'm new to git and I haven't been able to create commit messages in either vim or textmate(changed core.editor to mate). I can create commit messages when I use the -m option, but I like creating multiple-line messages and it's easier to do it with a fresh line-break in the terminal.

Using textmate I saved and closed the textmate file that pops up after $git commit -a, but git responds that the commit was terminated due to an empty message.

I am not familiar with VIM, can change modes, but none of the key combos I tried worked.

Thank you!, John