Except in Roblox or Minecraft.
Roblox:
1. Open cheat engine.
2. Set process to roblox.
3. Search for some line that would be in a script being run on the server.
4. Type in what ever script you want to execute.
5. Submit changes.
6. Script executes for everyone on the server.
7. You can make the server do whatever you want.
Minecraft:
1. Get custom client.
2. Use it to fly around and walk though walls and stuff.