Now that we've named the characters, what do you need to know next? There are several things and probably a slew more.
The character's physical appearance. Now this is more than hair or eye color. Think about their features. Are they even, pleasing, ugly, anything about this that can give your character a face. Then there's the height. Tall, short or average? Are they thin to the point of emaciation or robust or obese. The there's much that goes to the character in this. Think of Ickabod Crane, His physical appearance immediately gives a picture of the person. Or how about the woman too beautiful to be believed. Think about their hands. Those of someone capable of thin and fluttery. One can show a lot by hands or feet. In romances often the heroine or hero's physical presence sets off the story. So look at these things with a eye to bringing your character alive.
What is their chosen career? I write a lot about doctors and nurses but there is more to the career choice than a stereotypical picture. Often a choice of career leads to their education, their status in life and their way of seeing situations. Where were they educated? Are they buried in college loans? Did their wealthy family or their self-sacrificing parents pay for their career. All of these things make a character what they are. So give this area much thought for you want your character to leap off the page so people will believe he or she is alive in the story.