Males naturally use the chest voice and have to tighten the muscles to push their voice into the head voice for the higher pitch head voice. Women normally tighten the muscles and have to relax them in order to use the chest voice. Singers are trained to do the so they can cover a greater range. Karen Carpenter was noted for singing in the chest voice and the Carpenters referred to it as her money voice.
You should be able to put your hand above the larynx and feel if there is tension the muscles. If there is, just try to relax your body and that area. Try doing a relaxes aaahhhhh at a low volume for starter to get a feel for the voice. Once you can reproduce this, attempt to speak while maintaining the relaxed state. When done correctly, you will feel vibration from around your larynx area instead of the mouth/facial mask area that you may be used to.