Go through each of them and start maining whatever feels comfortable to you. Usually its Ryu or Ken. Some prefer Guile and so on. Learn a secondary or even a third character after (you wont get bored using the same guy at every battle with friends). Getting into it is easy. Very easy for SFIV, actually. Learning the intricacies of the system takes a lot of time, dedication and practice. Start with just getting familiar then get to know the characters basic moves then keep on going to learn things like frame advantages, properties etc.
SSFIV: Guy, Fei-Long
Tekken 6: Miguel, Leo, Kazuya