Сажать/посадить: to seat, plant, imprison, put
In English, I don't have much occasion to use the verb "to seat." In fact, I think the last time I used it was a year or so ago: "Even though we made a reservation, the maitre d' didn't seat us right away."
On the other hand, in Russian I seat things all the time. That is, I use the verb pair сажать/посадить almost every day.
First of all, you use сажать/посадить when you are putting someone in a sitting position. Он посадил меня на диван и стал рассказывать о том, что случилось. (He seated me on the couch and began to tell me what happened.) Or: Я посадила ребенка к себе на колени и стала читать ему книгу. (I put the child on my lap and began to read him a book.)
And since you sit on airplanes, trains, cars and other forms of transport, you are "seated" when you board them. Hence the word посадка (boarding) and посадочный талон (boarding pass) and the announcements you hear at the airport: Идёт посадка на рейс … (Boarding flight number … ).
That's what passengers do. But planes also "sit" or are "seated" — that is, they land: Самолёт садился далеко из терминала (The plane put down far from the terminal). Пилот посадил самолёт на Гудзон (The pilot landed the plane on the Hudson). And so when посадка is used to describe planes and not passengers, it means a landing: Боинг совершил аварийную посадку (The Boeing made an emergency landing).
You also use this verb pair when placing something that "sits." For example, since in Russian birds sit (сидят), you would say: Посади попугая обратно в клетку (Put the parrot back in his cage). And since you "sit" on a diet in Russian (сидеть на диете), during a checkup a doctor might say: Я посажу вас на строгую диету — надо скинуть несколько килограммов (I'm putting you on a strict diet — you've got to lose several kilos).
But you already know that — it's all the fault of your сидячий образ жизни (your sedentary lifestyle).
Come springtime, that will change: You'll be at the dacha for the planting season. For some reason, you "seat" plants in Russian: Каждый год я сажаю очень много цветов, но в этом году я посажу яблоню и грушу (Every year I plant a lot of flowers, but this year I'm going to put in an apple tree and a pear tree).
If the seating arrangement in the garden is clear, in the kitchen it isn't. It would seem that you "seat" pies, bread, turkeys and cakes in the oven. Если хлеб печётся в русской печке, то он сажается прямо в чисто выметенную печь на под (If the bread is baked in a traditional Russian stove, it is placed right on the bottom of a cleanly brushed oven). But I've found recipes that use the term поставить (to place upright) or even положить (to lay). In any case, you shouldn't be baking bread when you're trying to lose weight.
If being on a diet is like being put in food jail, it should not come as a surprise that since you "sit" in jail (сидеть в тюрьме), you are "seated" there. Мэра посадили на три года за взятку (The mayor was imprisoned for three years for bribe-taking).
Jailing, landing, boarding, seating, planting, … tell me again about my сидячий образ жизни?