Gifted subs are subscriptions that either you or someone else can buy for a viewer without a sub in the chat.
Unfortunately the option to subscribe via Twitch Prime is not currently available on subs.
You can switch over by going to the channel page, clicking the green Subscribed button in the upper right corner, and selecting your new option.
How much does a streamer make per sub? While a Tier 1 sub is worth one subscriber count, the Tier 2 sub is worth two subscriber counts, and the Tier 3 sub is worth six toward the number of subscribers needed to unlock new emote tiers.