If you are using the same materials as me, then cut the white pieces first and then the black pieces. 

Glue the front white cross to one of the Black crosses and then glue the other black cross to them with black side facing out.

Glue the white small base piece to the larger black piece making sure the slot aligns. Then attach the stand to the cross.

OR 

I placed the front and back crosses into the two stands without glue and then wedged the middle cross in between them and with a gentle tap of a rubber hammer secured them in the base. I then applied super glue to the middle cross on either side at the top, applied pressure and they were joined.