Scientific name: order: lepidoptera
Butterflies are a kind of insect that changes completely as it goes through its life. A butterfly starts as an egg, which hatches into a caterpillar. Caterpillars spend all of their time eating leaves from their favourite plants. When they are old enough, caterpillars spin a cocoon and while they are asleep inside it, they change into a butterfly. Butterflies eat nectar from flowers, and live for a much, much shorter time than caterpillars.
Scientific name: cucurbita moschata
The butternut squash or butternut pumpkin can be eaten roasted, mashed, or made into soup. It is a quite small, sweet, mild variety of squash.
A button is a small, usually flat object that you use to keep your clothes shut. Buttons can be made of wood, metal shell or plastic. There is usually some holes through the button or a loop under the button so they can be stitched to your clothes. You fasten a button by passing it through a matching hole.
A buttress is a structure built against a wall, at right angles to it, that thickens and supports the wall. They were commonly used when building large churches. The flying buttress is a type of buttress set away from the wall it supports, supporting the wall by an arch between it and the wall.
You buy something when you give someone else some money in exchange for it. The man in the picture is in a shop buying some goods. The opposite of buy is sell. The past tense of buy is bought.
By might mean near, as in "she was sitting by the lake". It might also be used to indicate who did something, for example "this book was written by my brother".