First and foremost: Donations and voluntary financial offerings from believers (e.g. tithes, thanks-offerings, donations for mission) are a pleasing scent for God. 
Nevertheless, they’re also an expression of gratefulness and of commitment of faith and show determination to participate in the local and universal ministry of the Church of Jesus Christ.
Donations and offerings are used for various church ministries and projects, for example:
monthly rent for the church facilities as well as for maintenance, payments for train and tram tickets for refugees who attend church services and events, financial or material help for church members in need, expenses for (seasonal) church events and projects, church equipment, evangelization and mission.

Through these offerings and donations believers actively participate in the building of the Kingdom of God.