Maracas get their sound from many loose objects, such as seeds, inside a hollow container (such as a gourd). It is usually on a stick handle.
These maracas are not better or worse than others -- just different.
The tops have been hollowed out and small containers of seeds have been placed inside them. Variations in the seeds used and/or the containers for them make variations in the sound. In the absence of maraca seeds, try beans, rice, popcorn, BB's, etc.
The foam not only acts as a handle, but it can also be used as a sort of drum stick, for tapping against one's body, or other objects to get that sound as an overlay on the maraca sound.
In the last step, you can hear the sound they make.
Step 1: Shaping the Styrofoam
I cut the basic shape out with a hand saw first, and then touched it up with a course file and sandpaper. It is very easy to shape.
Beware of the little flakes of Styrofoam that will land on the floor and blow all over the place, if you let them. I work indoors where there is no breeze and catch them in a big plastic box as they fall. I mix the foam "sawdust" with cement later, as a filler material, and use it in sculpture.
One could decorate the Styrofoam, I suppose, to make it prettier. I don't mind bare bones functionality in this case. The sound is more important to me than the looks.
Step 2: The Seeds
I put the seeds in a plastic film can (In this digital world, are they antiques yet?), and buried the can inside the foam by cutting off the top and drilling a hole with a wood bit. After placing the can in the hole, a little wood glue stuck the top back on again. I held it temporarily with masking tape until the glue dried.
Step 3: Hear the Maracas
I hope you enjoy hearing the Styrofoam maracas