This type of account is called a stocks & shares ISA, where you can invest in funds (shares or bonds from various companies pooled into one investment), bonds (basically a loan to a company or a government), and if needed shares in individual companies.
Stocks & shares ISAs are typically managed by an online service (often called an online broker or platform), fund management group or fund supermarket.
The value of the investment can go down as well as up and you may not get back as much as you put in. If you wish to open a stocks & shares ISA, you need to be aware that many of these companies charge a fee for you to open and hold a stocks & shares ISA. Some even charge you if you want to change any of your investments, withdraw your money or move it to another company.
Some stocks & shares ISA providers may allow you to hold some of your allowance as cash within the stocks & shares ISA. But you're free to open separate accounts if you prefer.
In the tax year 17/18 the current ISA allowance is £20,000 and will stay the same in 18/19 tax year. This makes a worthwhile tax efficient incentive that can be totally invested in stocks & shares or split into a cash ISA account. The process of investment must be done with care. An online process can offer guidance; however, a local Financial Adviser will be able to give professional depth to the initial and ongoing investment strategy.