The highball and collins glasses are very similar to each other. In the photo above, the glass on the left is a collins glass and the one on the right is a highball glass. They each hold around the same volume - between 8 and 12 ounces - though the collins tends to be taller and more narrow, more of a chimney shape than the stouter highball glass, which usually tops off at 10 ounces.
The glass in the middle is an example of a sort of hybrid of these two glasses: the same volume with a little detail in the style.
*A Must-Have Glass
The highball glass is a style that every bar should have. The collins glass is not necessary, though convenient. The two can be used interchangeably.
These tall glasses are typically used for 'tall' mixed drinks and filled with an abundance of ice. Many times, the drinks are built directly in the glass by pouring the ingredients over top of the ice and stirring. The simplest of these drinks will often have a shot of liquor topped with fruit juices and/or sodas to fill the glass.
Highball glass examples:
Collins glass examples: