The good news is that it's pretty hard to break the machine using the wrong mill. You might break an end mill (or many....one of these days I'll post my box of broken tools), but it's pretty hard to actually hurt the machine. You can stall it, you can get the servos to skip, but it's pretty trivial to recover (turn it off, turn it on, and restart all the software). You can wreck the project, but it's hard to actually damage the machine.
In general, use a square end mill, up cut, unless you know you need something else. The up cut pulls the chips out of the cut better (but also pulls up on the material some, which is why down-cut exists for special cases). The conical and v-bit tools have special uses. The ball-end tools are generally but not always, for 3d machining. For your snowflakes, almost surely the square tool...assuming these are 2d/2.5d parts.
You want to use the largest tool you can get away with - if you don't have any details smaller than .25", use the .25" mill. If you have smaller details use the 1/8" tool. There is a speed-n-feed chart here: http://carbide3d.com/docs/support/ ... you're going to need this...maybe not right this second...but you'll need it eventually.
When you get a little further along, you can look at how to use the .25" for roughing, and the .125" for finish pass (with a tool change). It's not hard, but if you're just getting started, it's one more thing to mess with, so get comfortable first with just one tool.