A select group is a small group of some of the best people or things of their kind.

If you describe something as select, you mean it has many desirable features, but is available only to people who have a lot of money or who belong to a high social class.

If you select something, you choose it from a number of things of the same kind.

If you select a file or a piece of text on a computer screen, you click on it so that it is marked in a different colour, usually in order for you to give the computer an instruction relating to that file or piece of text.