Powershell and TCC are on a par ... they're both Windows console applications ... they run in a Windows console. In a Powershell console, you can start TCC (just issue the command [path_to]tcc.exe); Powershell will be suspended while TCC runs (in the same console) and when you EXIT TCC, you'll be back at Powershell. You can so the reverse too ... start Powershell in a TCC console; it's the same thing.
TCMD is quite different, and not a console app. TCMD it a graphical user interface to console apps; it runs console apps hidden and shows you their oupput in a tabbed interface which may have many tabs, each running a console app. You can't run TCMD inside anything. But you can run Powershell and TCC inside TCMD(and more) ... in different tabs ... TCMD lets you switch between the tabs.
You can start Powershell in al the ways you can start any application ... start button, run dialog (Win+R), desktop shortcut, double-click on powershell.exe in explorer, issue "powershell.exe" (possibly with a path) at the TCC prompt, configure a TCMD tab to run "powershell.exe" (possibly with a path) ... (the list goes on).