In the second season of Riot's League of Legends there will be two main changes, ranked teams and summoner spells.

1.   The first new feature of Season Two are the ranked teams. You can build up a permanent team including your own team name and ELO Rating. This ELO Rating is just a special number given to you to determine your ranking compared to other players. One could say that it displays your skill.
For better organisation, each ranked team will need an own captain with the power to invite or kick new members.

2.   The second big update include the summoner spells like Flash or Heal, here are the changes listed:

• Flash: Gets reduced range
• Clairvoyance: Will get increased cooldown
• Heal: Will be more useful in late game (for example Heal could restore 10% of your health instead of just 200)
• Ignite and Exhaust: Will be removed by Cleanse
• Fortify and Rally: Completely removed by new options, futher info is unknown so far
• Surge: NEW SPELL. Activation gives your champion an aura, increasing combat effectiveness for you and your allies 
• Promote: NEW SPELL, but known in Dominion. You can use it to buff a single minion, increasing its range, armor, and magic resistance, and health. 

Source: leagueoflegends.com