The powers of Council shall be legislative only. Council shall perform no administrative duties and shall neither appoint nor confirm any officer or employee in the City Government, except those of its own body, unless otherwise provided by the City Charter. All contracts requiring the authority of Council for their execution shall be entered into and conducted into performance by the board or officers having charge of the matters to which they relate. After authority to make the contracts has been given and the necessary appropriation made, Council shall take no further action.