bend down
The German phrase "sich bücken" is the equivalent of "bend down" in English. It is a reflexive verb, which means that the subject is also the object of the action. It is used when you want to express the action of lowering your upper body by bending at the waist, typically to pick something up from the ground or to avoid hitting your head on something.
He has to bend over to tie his shoes.
In this sentence, 'sich bücken' is presented in an infinitive form combined with 'muss' which means 'has to'. It represents a necessary action that a person 'he', in this case, must do, which is bending over to tie his shoes.
When cleaning, you have to bend over to reach the floor.
This sentence shows 'sich bücken' in the context of a cleaning activity. In order to reach the floor, a person (indicated as 'you' in English) must bend over, illustrating a physical requirement of this particular task.
She bends over to pick up her child's toy.
Here, 'sich bücken' is used to describe a movement that 'she' - a woman, presumably the mother, needs to make in order to pick up her child's toy. The conjunction 'um' connects 'sich bücken' with the purpose of the bending over action.