Participation in Mass is an essential part of being Catholic. Liturgical practices
incorporating the Eucharist, scripture, music, and prayer bring together a community of Christ that reaches inward to provide strength to fellow members and encourages outreach and service in the world outside of the Church. Joining in the Mass fully involves us as members of the Body of Christ, allowing us to live out our calling to be Christ to others.
When Mass is not available or one is unable to attend due to health or other grave reason, Catholics are encouraged to view to Mass online or through television, or listen over the radio and to make a Spiritual Communion.
Four Steps for Spiritual Communion
1. Make an act of faith: come up with your own prayer or use a traditional one to express the Lord your faith in his real presence in Eucharist.
2. Make an act of love: say a prayer that expresses your love and gratitude to the Lord. Thank Him for his infinite love as well.
3. Express your desire to receive Him: as you are not able to physically receive the Lord, express your desire to receive Him in your heart.
4. Invite Jesus to come into your heart: with a humble and contrite heart we ask the Lord to come to you just as He would if you were able to receive the sacrament.
Source: http://catholic.net/op/articles/3953/cat/1249/the-importance-of-making-a-spiritual-communion-.html