You need to be editing an HTML file. (You can see what Sublime thinks the syntax of the current file is on the bottom right corner). An HTML file is either one with an appropriate extension (.html, .htm, etc.) or one where you've changed the syntax to HTML via the menu or the command palette.
Then, just type
head (or any other tag) and press
tab. If it doesn't, you may have turned it off. Inspect your settings under the menu
Preferences > Settings - User.
There are other packages (Tag, Emmet, etc.) which can extend this functionality
Hope this helps,