First, some terminology. Chamfering refers to both the inside AND outside edge of the case mouth. Reaming is making the inside of a round hole larger, reaming a brass case to reduce thickness of the neck.
Most chamfer tools are a combo tool for both the inside and outside edge of the case mouth. Just about all of them have a fairly abrupt angle for both, 45 degrees. Lyman makes what they call a VLD inside chamfer tool. It's angle is very long, 75 degrees.
http://www.midwayusa.com/product/342199/lyman-chamfer-tool-vld-very-low-drag
http://www.midwayusa.com/product/211588/lyman-outside-chamfer-and-deburring-tool
Third choice is the Lyman combo tool that includes the VLD inside chamfer tool, outside chamfer, large and small primer pocket cleaner, and large and small military primer crimp removers;
http://www.midwayusa.com/product/135615/lyman-case-prep-multi-tool
Or, you can get the standard lyman 45 degree chamfer tool;
http://www.midwayusa.com/product/284379/lyman-chamfer-and-deburring-tool-22-to-45-caliber
Any of these is real simple to use. You rotate them when in contact with the case mouth, then flip it over and do the other surface. IMPORTANT, you do NOT want to make the mouth of the case look sharp like a like a leather punch. You just want to rid the mouth of the burr caused by trimming.
The VLD chamfer tool is better because the long taper allows any bullet to enter the neck easily. The standard 45 degree chamfer is rather abrupt, it will shave copper off most bullets while seating them.
I use the lee system to trim all my brass. The case spinner turns the case while I hold the cutter/pilot against the mouth, I use a cordless drill. I then run the drill slower while holding the chamfer tool against the mouth while the drill turns the case. I can also use a flash hole deburring tool at the same time. I finish while holding a pad of 0000 steel wool on the spinning case. It'll knock yer eyes out with the shine!