The structures palette contains many different basic structures commonly found in mathematical expressions, including subscripts, exponents, fractions, radicals, and limits.
The superscripts, subscripts, and prime symbols in the first row of this palette are normally applied to other symbols that are already part of an equation. To insert any one of these, the caret should be moved to the location where it should appear before it is selected from the palette. The base symbol should not be selected because it would be replaced by the inserted structure.
The orange box at the end of the third row is an inline group, which is a stack with no upper or lower limits. Inline groups can be used for a number of different purposes, but the most common is to create a new set of drawing anchors that fit the grouped expression.