In .gitignore I specified .zip and it didn't work.
But when I did *.zip it filtered my files to be commited.
What's the difference between these two?
.gitignore is looking for file names or glob patterns, not extensions.
Without the wildcard, .zip in your .gitignore is only matching a literal file called .zip, which is unlikely to exist, but if you were to create it (say by calling touch .zip you'd find that git correctly ignores it.