After 1D wavelet decomposition you will obtain a approximate low frequency and a detail high frequency components of your observation signal in time.
Example code from Matlab Help load noisdopp; [A,D] = dwt(noisdopp,'sym4');
A is your (Approximate) low frequency signal D is your (Detail) high frequency signal sym4 is the mother wavelet (namely symlet 4) used to decompose the signal. It determine how well it decompose the signal. So you need to know the observation signal and application well for you to choose the right mother wavelet. You will notice the resultant decompose time samples are half of the original time sample.
