A stocks & shares ISA is a good place to start your investment journey. A share is a small unit of the value of a company. A share is simply a divided-up unit of the value of a company. For example, if a company is worth £100 million, and there are 50 million shares, each share is worth £2 (usually listed as 200p). Those shares can, and do, go up and down in value for various reasons ...