2.2.12.2 needs to be read in conjunction with the table in 2.2.12.3.
If you state your intentions and ATC *acknowledge* your call and give nothing else, you must comply with your stated intentions (ie although they haven't said 'you are cleared', you have been cleared to enter D and your 'clearance' is effectively 'do what you said you would do'). Also you *can* descend to join the circuit if no altitude instructions subsequently given.
If ATC give you specific instructions (which seems to be the more common case), you are cleared to enter D and your clearance is to do what you were instructed (although you *can* descend if no altitude instructions given by ATC).
Also VFR aircraft operating in D are responsible for maintaining themselves in VMC.