An SSD replaces your hard drive. Unfortunately they are kind of small in comparison, so you may need to stick with a hard drive. A SSD uses flash memory like a USB drive, except in place of your hard drive. The speed increase is phenominal. This will replace your drive so you will need to reload OS X which is easy thanks to Internet Recovery.
Kingston makes a 64GB model that is decent, I have one in an older original MacBook and it feels so much snappier. http://www.newegg.com/Product/Product.aspx?Item=N82E16820139949
http://www.newegg.com/Product/Product.aspx?Item=N82E16820226318
They vary in all different capacities and speeds. Not all SSD's are created equal.
Follow the instructions in your MacBooks manual to upgrade the drive.
You will need a 2.5 inch SATAIII SSD if you choose to go that way.
Between the SSD and the RAM upgrade you have a beast of a machine.