first, try looking at some random pieces ...hygrid?center=random and looking for "OPEN!..." gray squares. if you are logined, you can reserve this square, and add to it. (yup, it is 100 x 100 pixels.) blending is encourage, generally. -grin-
as for viewing the whole image -- well, the nature of hygrid is non-planar, or multi-dimensional, i suppose. in other words, if you travel LEFT then UP, it is not the same as traveling UP then LEFT! if that makes sense! so it is not a tiled-quilt, but rather a series of twisted connected images that at any given time you are vieiwing some small part of. confusing, no? wow.
and it even gets more confusing, as you can create "links" or "wormholes", which are images that connect from ONE PART of hygrid to ANOTHER. very confusing!
maybe the best way to start is using the simplest "cross" view: ...hygrid?center=random&layout=6
also, the hygrid help can give a little more insight. its quite fun, and addictive, in its own right.