When visiting friends or relatives in the Schengen zone, you will need to prove that they are expecting you and you have the funds to be able to remain in the country for the duration of your trip. This takes the form of a written formal invitation signed by the relative or friend that you will be visiting, as well as copies of their passport or residency permit.
Whoever will be funding the trip, whether this is the applicant or the relative or friend they are visiting, needs to submit proof of their financial status including information that shows they have the required funds.