Yes you have to use triangle... because even the square consists of two triangles, as you already know. Triangle is the simplest shape in a 3D world so you have to build everything using those. And ofcourse you have to manually build those triangles... think of it this way... if you have lot's of vertices then there's no way blitz is going to know how you want to connect those vertices eg. what kind of shape you want to make... so you have to triangulate your mesh by hand.