OK, the Turtle has variants, but here is an example…
Main territories are Germany and Eastern. Secondary are Southern and Western.
You stack Eastern to be a can;t lose block of forces against Russia. You use small numbers of INF and you AF to trade Karelia, Bel, Ukraine. You keep Southern secure by preventing access to it, and you secure Western with enough forces, and perhaps basing AF there, to prevent a direct Allied landing. You also preserve your Baltic fleet (where possible) as a shield against the Allied fleets.
You let Russia make some early gains… trading hard, but never exposing high value units like ART and ARM. You keep building land forces to float to Eastern (and Western as needed). Once Russia makes a STRONG move into Karelia, Bel, Ukraine… you counter with the entire mass from Eastern, ideally destroying most of Russia’s offensive forces leaving them with only INF (and perhaps a few FIGs), then you start a spearhead drive for Moscow… going via Caucuses if Japan is strong on the southern prong to lend support.
To prevent loss of income, you insure adequate AF for trading as noted above (so you are only ever down Norway and West Russia) and you keep Africa supplied as long as possible to get as much UK income from there as you can.
Basically, you keep Germany building and secure while Japan makes its gains in Asia, then you pounce on any openning Russia gives you and engage in a two-direction smash on Russia… waiting for Japan to be in range before Germany starts going offensive instead of driving on Russia right away.
The main advantage of the Turtle is that Germany is building massive INF almost exclusively, preserving their initial 8 or so ARM and their AF to use to provide offensive punch when the time comes, and huge numbers of INF to eat up defender hits and provide holding power when you do move, to serve as sacrifices for trading, and to prevent UK and US from attempting amphibs. So Germany can build on the cheap… not having to replace lost ARM or AF because it basically is never risked on the offensive…until the scales are so much in their favor that their main drive cannot be stopped.