I'm guessing you mean through console. Not sure on ban but kicking is "FindClientByName(name).delete("reason");" or "FindClientByBL_ID(id).delete("reason");" capitalization doesn't matter.
If you mean in-game though, get to the admin menu either by pressing escape and clicking admin menu or by pressing ctrl a. Click on the player's name and hit ban. Set the time (there's a checkbox for perma) and type the reason, then press ban. If they've already left your server and you didn't catch their ID, click the button at the bottom right of the admin menu, the brick menu. From here you see everyone who's been in your server during the current map, an you can also click their name and press clear to clear all of their bricks... or clear all bricks. But anyways you can click their name and press ban to ban them the same way as explained before. The ban reasons and times are carried over in both menus so instaban is a go. Also, like others were saying, there's a command for banning that goes like this: "/ban (ID: id) (time in minutes, -1 for perma) reason". Example: "/ban (ID: 0) -1 snake-nose". Sadly ban reasons can only be one word using the command, whether with quotations around it or not, so I suggest using underscores to replace spaces.
I'm sure you knew some to most of this, but I hope I filled in the parts you didn't already understand. :)
