It's hard for me to bite down while the orthodontists put on the bands(metal rings) on my molars. any tips?

Molar braces: When placing the bands, some biting pressure is required to move the band into its ideal position. If you could not bite down easily, perhaps the band was not fully seated on the tooth or your tooth is not straight. When the tooth moves into a better position, you will be able to more easily bite.

Don't bite: If you are trying to bite down while the orthodontist is putting on the bands he will be very upset when you bite his fingers so don't bite down while he is putting on the bands. If you are talking about after he placed the bands then say so. The teeth will move and it will be difficult to bite for a while. If it is right away the bands may be high and need adjustments.

Band driver: I take this question to refer to the weakness or inability to bite sufficiently to fit/seat the band as your appliances were being fabricated: I use an mechanical hand held"jack-hammer" which is not painful, but helps drive the band into place. Alternatively one could bond a bracket as another option.