For a simple and very good high carbon steel to use for knives get some plain steel in the 1070 to 1084 class. This is one of the simplest steels to learn on especially for a good simple heat treat - a plus this class is the closest modern steel to period steels that is commercially available, based on several tests done on period steels of the pre-1860 era.
IMO one for the best sources for good knife steel is here:
http://newjerseysteelbaron.com/shop/product-category/high-carbon-steel/
While good files like Nicholson or Black Diamond brands files can be used they are generally made of 1095 or W1/W2 which are much more difficult to get a GOOD heat treat with just basic home equipment and IMO is best left to those with the proper equipment and experience.
Scrap steel of varying types such as auto springs, plow discs, etc can be a good source for blades, but once again it's best left to those with the experience in using unknown steels.
At this point using a good commercial steel like 1084 (after 50 years making knives it's still my favorite) will make the learning curve MUCH easier...
Here's the basics for heat treating 1084:
http://usaknifemaker.com/metals-c-...-c-93-35/heat-treat-information-data-faq.html
The cheap low carbon steel from the big box stress though can be used for grinding/shaping practice and is much less expensive - it can also be used for various fittings such as cross guards.