Can you tell me about the differences in Lutheran Churches?

There are some significant differences in the membership of the Lutheran Church. Three of the different denominations that consider themselves Lutheran include:

Wisconsin Evangelical Lutheran Synod (WELS)  
Lutheran Church — Missouri Synod (LCMS)
and the Evangelical Lutheran Church in America (ELCA)

According to the Handbook of Denominations in the United States (Nashville: Abingdon Press, 2010), here are some facts and figures:
 
The ELCA has 4.7 million members in 10,400 congregations. “The ELCA promotes the Lutheran theological and liturgical tradition while allowing greater freedom for laity and clergy to address contemporary social and intellectual concerns than most other Lutheran denominations. It also engages in extensive ministries to promote both greater social justice and mercy in the world.” (p. 108) The ELCA ordains women and has entered into ecumenical full communion agreements with the Presbyterian Church USA, the United Church of Christ, the Moravian Church, the United Methodist Church, and the Episcopal Church. For more, see the ELCA website: http://www.elca.org.
 
The Lutheran Church — Missouri Synod has 2.4 million members in 6,000 congregations. “Though the denomination participates in many ecumenical dialogues, it does not share in communion with churches unless there is agreement in the confession of the Gospel in all articles.” (p. 110) For more, see the LCMS website: http://www.lcms.org.

The Wisconsin Evangelical Lutheran Synod has 400,000 members in 1,300 congregations. “This synod subscribes to confessional Lutheranism and is committed without reservation to the inspiration and infallibility of Holy Scripture. It seeks fellowship with those who believe that full agreement in doctrine and practice is necessary for biblical fellowship.” (p. 110) For more, see the WELS website: http://www.wels.org.