What additional features do you get after spending five dollars on Steam?
According to Steam's help page:
Limited users are prevented from accessing several features on Steam, including but not limited to:
- Sending friend and group invites
- Requesting access to groups
- Opening group chat
- Voting on Steam Reviews and Workshop items
- Participating in the Steam Market
- Trading Steam Community items (trading cards, booster packs, gems, etc.)
- Posting frequently in the Steam Discussions
- Gaining Steam Profile Levels (Locked to level 0) and Trading Cards
- Submitting content on the Steam Workshop
- Posting in an item's Steam Workshop Discussions
- Accessing the Steam Web API
- Using browser and mobile chat
- Adding public artwork and screenshots
- Adding messages to trade offers
- Creating Steam groups
- Counting towards Steam group membership
So, I assume you are able to do the above after spending five dollars.
According to this article by Valve, this is what a "premium" account gets over a "free" (officially called "limited account") one:
- Sending friend and group invites
- Requesting access to groups
- Opening group chat
- Voting on Steam Reviews and Workshop items
- Participating in the Steam Market
- Trading Steam Community items (trading cards, booster packs, gems, etc.)
- Posting frequently in the Steam Discussions
- Gaining Steam Profile Levels (Locked to level 0) and Trading Cards
- Submitting content on the Steam Workshop
- Posting in an item's Steam Workshop Discussions
- Accessing the Steam Web API
- Using browser and mobile chat
- Adding public artwork and screenshots
- Adding messages to trade offers
- Creating Steam groups
- Counting towards Steam group membership