Some of the features:
- The first four missions of the StarCraft II: Wings of Liberty single-player campaign, including Mar Sara 1-3 and the choice to
embark on Tychus’s first mission or Dr. Hansen’s first mission.
- The first two Challenges: Tactical Command and Covert Ops.
- Access to the terran race in Custom Games and Single-Player vs. AI.
- Access to the following custom maps (map selection may rotate over time):
- Xel’Naga Caverns
- Shattered Temple
- Discord IV
- High Orbit
And some of the restrictions:
Q. What are the restrictions of StarCraft II: Starter Edition?
A. Starter Edition players can only play up to the fourth campaign
mission, and most Challenge Missions are unavailable. Starter Edition
players are also unable to use versus and co-op matchmaking, most
custom maps, chat channels, and the party system. Publishing custom
maps to Battle.net is also restricted, and offline play is unavailable
to Starter Edition players. For single-player and custom games,
Starter Edition players may only choose the Terran race.
You can find this information and more here.
This means you can not play ranked games, but you can play vs your friends in the 4 maps that are available for starter edition but only as Terran.
There is an exception if your friends own Heart of the Swarm, which includes a Spawning feature. You may party with any Heart of the Swarm friend to temporarily upgrade your Starter Edition to a Spawned Edition of the game. While spawned, you may play any multiplayer game type and map with them, including ranked games. As a starter player, your race will still be locked to Terran. When you leave the party, you will be downgraded back to Starter Edition.