Slime user FAQ:

• M-x slime?
  M-x Start Slave Process
  
• Can I also debug the editor itself? Yes, it can connect to itself as a slive:
  M-x Start Slave Thread
  
• It doesn’t ask me for the Lisp to run!
  To run a Lisp other than the Editor’s own core, I recommend M-x Start Slave Using Clbuild
  (There’s also C-u M-x Start Slave Process, but this line is too short to explain it.)
  
• Keybindings?
  Things that should work: Compile Defun (C-c C-c), Compile Buffer File (C-c C-k), Slave Apropos (C-c ?), Find Definition (M-.), Who Calls (C-c C-w C-c) and other xref commands.
  
• Selector?
  There is the equivalent of the slime selector bound to C-c SPC. For example, C-c SPC r will bring up the current slave’s REPL, C-c SPC c the list of slaves, etc.
  
• REPL commands?
  Hemlock uses PREPL, which is a portable version of sb-aclrepl.
  You can use PREPL outside of Hemlock. When running in Hemlock, the editor overrides some PREPL commands though.
  For example, :apropos foo will open a buffer when running in Hemlock.
  
• Can I debug Hemlock using Slime?
  Of course, at least if swank is installed. There is even a command for that: M-x Start Swank Server