To my understanding, enabling the specific 'strategy' enables all of the parameters below it (the highlighted green text.) It's a little confusing and not very well conveyed but it basically means "you're picking this set of bonuses."

Thanks bro!

As was already said, each strategy provides the green benefits which pile up as you unlock them. Each is tied to a particular character and changes how you can play your tanks. They nudge you in a certain direction which you can either use to specialise in a certain way OR to cover for the weaknesses of your playstyle or chosen tank.

I will describe them in a bit more detail and also add how I use them.

1) "Steady Growth"/Commissar:

The "basic" strategy. The only one that does not benefit from picking specific skills or turrets. Gives you more starting resources, bonus to the persistence resources (both types), increases turret drops, and adds more crew and makes crew more durable. So boost for the most common/generic things.

I pick this one if I don't want any other strategy. Also a great pick if you pick a vehicle that requires a lot of allies (money helps), might need more crew (a big tank where losing once costs a lot of crew or a weak vehicle that might require as many tries as you can get). The additional turrets and money also helps for some multi-turreted tanks since you can get better turrets faster (and replace the secondary MGs with something with more dakka). Also pick this to unlock other strategies faster.

2) "The bigger, the better"/Sophia:

Focuses on HE, money, and Sophia. Basically pick mostly HE turrets (more damage and bigger boom for that run) and her skills (a lot of HE guns have slow reload so this bonus is crucial). Getting more money from direct kills and discount in shops synergizes well.

I pick this mostly with HE or rocket vehicles. If you know what you are doing you are basically firing small nukes at the end... But that reload and damage will help on almost anything. One of my two favorite strategies.

3) "Determination"/Sunday:

MG, HVAP (and a bit of rockets), mobility, and Sunday. Again, pick such weapons and skills. This benefits mostly the weapons with multiple shots before reloading. And the mobility bonuses makes smaller or nimble vehicles insanely mobile and eliminates the clunkiness of bigger tanks.

Careful on the 2. bonus. Sometimes you want a magazine weapon but don't want to increase the ammo too much. There is a skill that doubles your penetration for the last round and increasing your total ammo makes these "armor shredding" shots less common. Also there is a thing as "too mobile" or "too responsive". But this strategy allows you to pick things you normally avoid because they decrease mobility too much - thus allowing for some insane armor if you go this route.

4) "Panzer ace!"/Yulia:

AP, APCR, Yulia. Again, pick these weapons and skills. Grants direct kill bonuses, extra crti chance (so you can have 50 %+ even when moving), piercing on everything, and insane reload speed.

One of my two favorite strategies. With this you can spam very powerful piercing shots and Yulia can even aim for you. I use this mainly on tanks with a single AP/APCR turret or on MTTs. The amount of firepower you can get with this one is insane. Perhaps less showy than big booms Sophia provides but still insane.

5) "No limits"/Maria:

Speed is the name of the game. Speed, mobility, and Maria. Pcik everything related to Maria and mobility, Also adds extra crew and ramming capabilities and turbo. Not tied to any turret type.

This one is very specific and oriented towards ramming. I admit I dislike ramming (I will either nuke you or just pummel you into submission from afar) so I don't use this one much. But it makes ramming that much easier. You could also use it on big clunky vehicles since it adds speed, mobility, ramming efficiency and extra crew.