These are diffraction spikes. They are an interference pattern caused by the the arms and shape of the telescope. 
They occur around whatever is bright enough in the image which in this case is all the stars that are within the milky way. These stars show up super bright because the Webb is trying to look for super dim objects in the deep field.
The spikes very near the star (horizontal and two diagonal ones) are the three arms and the inverted image of those 3 arms.
You can think of them as a type of "shadow" the telescope is casting.
The larger lines which form the 6 points are caused by the non circular shape of Webb also causing an interference pattern.
The geometry of the arms was chosen so that the diagonal spikes from the arms line up with the spikes from the shape of the telescope. This was done to minimize the effect.
It is worth noting that all the galaxies also have diffraction spikes but they are much dimmer due to the amount of light and diffuse due to the non point like nature of the extended objects.