Select the album containing the shot you want to caption.
Tap Edit at the bottom of the screen.
Select the shot you want to caption.
Tap the keyboard icon in the top right corner.
Tap the full screen text option.
Type your text.
Tap the thumbnail.
Drag the text to position.
Pinch your fingers to zoom.
Select text and tap Highlight to emphasize words.
Tap Save to apply changes.