You can send gifs via GIPHY by typing /giphy in chat followed the your search term.

You can mark an image as a spoiler when sending it by tapping the eye in the corner of the text entry before sending your message.

You can add a friend to your Favorites bar by long pressing on them in your Friends List, or tapping the header in a chat with them to open the settings page for that friend.

You can generate friend invite links by tapping the menu button in the top left of the app and selecting "Add a Friend" followed by "Invite Link". You can then generate a link and send it to your friend via text, or email.