Brigid's Cross is a symbol that has been around for quite sometime. It is associated with the Celtic Goddess known as Brigid and also with her saintly aspect. Traditionally, it is created from rushes but it can also be made from other materials. It is represented with four arms and a square shape in the middle and has associations with the sun. These are usually created on Imbolc or St. Brigid's Day as decoration and are a symbol of the Saint/Goddess. Making the cross itself can place a person into a meditative state. They were hung over doorways and windows as a symbol of protection.
If you're wanting to make your own, the best material to use when starting out are pipe cleaners. You'll need quite a few to get a good cross going. I recommend using at least 30. There are many online tutorials and one of them can be found here.
Here is one that I created for Imbolc: