x11 is not the default, to use it you will have to add this line to your .vimrc:
let g:slime_target = "x11"When you invoke vim-slime for the first time, you will have to designate a target window by clicking on it.
If SlimeConfig hangs without asking you to select a target terminal, you may not have xdotool installed.
If SlimeConfig works and you can send text to the terminal window running vim but not to other terminal windows, your terminal may be configured to ignore the XSendEvent events generated by xdotool by default. See the SENDEVENT NOTES section of the xdotool man page for details. Note also that allowing arbitrary programs to send text to your terminal to be executed is potentially a security vulnerability.