Composite materials that are used as reinforcements can be impregnated with resin ahead of time, are called prepregs.  You use a prepreg in manufacturing different composite parts by cutting it out and laying it onto your mold, shaping as required.  Since it has already been impregnated with resin, there are not any concerns with spreading the resin and curing agents on the dry materials while they are in the mold.

Pre-impregnated materials can be purchased from a composites supplier, or they can be made yourself.