Insert Minecraft Player Name?

How can I insert the names for commands or in the chat without having to write them out? I read with TAB. I tried it but it does not work, anyone suspects why?

You have to write the first letters of the name and then press the Tab key. Some servers have issued that, so try that on different servers if that does not work.

Okay, I'll test it. I play on griefergames. Should work there because the people in the chat at least write that it works