Here's what happens and what you do next:
1. The Blood on the Wall: The blood inscription appears in the girls' bathroom and reveals the opening to the Chamber of Secrets.
2. Moaning Myrtle: Harry encounters Moaning Myrtle, who is the first victim of the Chamber of Secrets.
3. Following the Trail: The blood trail leads from the bathroom through various areas of Hogwarts, and you must follow it.
4. The Chamber Entrance: Eventually, the blood trail will lead you to the Chamber of Secrets entrance.
5. The Chamber of Secrets: You'll then proceed into the Chamber, where you will face various challenges and eventually fight the Basilisk.
So, after the blood on the wall, you are essentially following the blood trail to the Chamber of Secrets. The blood trail will take you through various areas, including:
* The Library: You'll have to solve a puzzle with books to continue.
* The Potions Classroom: You'll need to brew a specific potion to proceed.
* The Defense Against the Dark Arts Classroom: You'll have to fight some Dementors.
The blood trail is your guide to the Chamber of Secrets.