Specifically for the 10.4.4 update, Apple introduced the ability to into your video. You can create these by going to Edit > Captions > Add Caption (or pressing Option-C ).
: With the title selected, open the Text Inspector in the top-right corner. Here you can change the font, size, color, alignment , and adding effects like drop shadows or glows .
: Press Control-T to instantly add a basic title at the playhead's position.