Teaming is often used to find players or to team with friends to recieve experience, When you invite someone to join your team you will be the team leader which means you will be the only one in the team able to kick and invite playeres into the team.
When your in a share team everyone in the team receive an additional 10% to all gained exp
When your in a team alone you get to keep all your own experience and also receive an extra addional exp for those people who want that extra little bit.
Leeching is when you have a character killing mobs in a share team and others in the party gain experience fast and level fast depending on level. To gain levels fast you have to have a party leader 100+ or someone who is very strong with good stats to recieve good experience the person who is not killing the mobs and gain the experience has to be a low.