A blood stone is a certain stone. Usually green with red specks though they are known to have other colors in them such as yellow and blue. They are my favorite stone and have a very warm energy about them.
A gemstone is a general term for a precious/semi-precious/gemstone. Its just another word.
As for Blood stone, what do you need it for?
Bloodstone has different metaphysical properties including helping with the blood and circulation in the body, energy balance, creativity, intuition, self esteem and anxiety.
You can atune your energies to the stone itself, and feel its energy flowing into you, and you can also carry it around in a pouch or your pocket, and have that stone influence your daily emotions/behaviors.
That's how you can use the stone's energy. I'm sure there are more ways, but these ways are more effective for me.