TLDR-

There are 2 types of bots

RNDbots

These are the bots in the world. They are randomly created, they are out in the open world, they quest, they do LFG, they do dungeons/raids, they do battlegrounds and flag for pvp, they shitpost in chat. They work like real players in the world. They log in and log off randomly, and sometimes get deleted and replaced by other bots. Don't get attached to them.

ALTbots

All other characters in YOUR account (that you can choose on the log in screen) are available as bots as well. They will not be out in the world, but you can invite them to your party.

To do this, type in chat .playerbots bot add NAME where NAME is your character's name, CAPS SENSITIVE. They will join your group, and follow you around. They will gain XP, they will do the quests you do, and act like normal party members. They will save their gear, you can log into them from the character screen, and they're smarter than RNDbots (they react better, have better AI, but still not perfect)

ALTbots are the best bet if you are doing progression. RNDbots are fine for dungeons and LFG. But if you want to do raids, ALTbots are better.

If you want to raid

You can use the chat commands found on the wiki at the beginning of this article. There is an addon to make that easier. Download this, and add it to your interface folder. It makes a GUI for controlling bots easier - https://github.com/Macx-Lio/MultiBot

How well the bots will do in a specific raid can be viewed at https://github.com/liyunfan1223/mod-playerbots/wiki/Playerbot-Raid-Completion-Status and https://github.com/mod-playerbots/mod-playerbots/wiki/Playerbot-Raid-Strategy-Guide

But, I can only have 10 characters on my account. How can I do 25 or 40 man raids?

You can link your accounts. One one account run the command .playerbots account setKey somePlayerDefinedSecurityKeyValue where somePlayerDefinedSecurityKeyValue is some passphrase you know. It's a password. And then on your other account run the command .playerbots account link ACCOUNTNAME somePlayerDefinedSecurityKeyValue where ACCOUNTNAME is the name you log in with to the game itself not a character name, and the password you typed in the first command after that, to link the accounts. You can verify this worked by running the command .playerbots account linkedAccounts Now you can use characters from both (or more) accounts as ALTbots. If you want to run 40 mans, you need 4 total accounts of characters.

If you want your ALTbot leveled up to your level

Create a ticket in game. A GM will respond. We will levelup your ALTbot(s) that you specify to your main character's level, or any level below that you specify. If you do not specify, we will level it up to the max level of the highest level character on your account on the realm.

Suggested commands

You can type maintenance into party, raid, or tell to your bot(s). This will cause your bot(s) to learn all available spells and skills, supplement consumables, enchant gear, and repair their gear. This can be done at any time. This is meant to simulate everyone returning to town to stock up on consumables, repair, etc.
If you type it in tell, only the one bot will do it. If you put it in party or raid chat, all bots will do it.

The autogear command is disabled. Send your ALTbot some gold, and goto the auction house and buy gear to equip it. It will auto-equip upgrades as it loots them from mobs or quests.

General Bot notes

Just like normal servers, a lot of characters in one area can cause lag. Deal with it. Like, if you're in AV and all 80 characters are fighting in a blob, expect some lag. This is running on a spare computer of mine. I'm not investing heavily into hardware for single digit number of players. QQ moar noob.