In addition to participating in the liturgy as an attentive member of the congregation, there are several ministries available to those who would like to serve in various ways.
You may offer or be asked to bring up the offertory gifts at Mass, or take up the collection, or greet people as they arrive at church. There are other ministries which need some training, or have basic requirements which need to be met. Those ministries are: Extraordinary Minister of Holy Communion (EMOHC), lector, altar server, and music minister.