Your standard account can be used if you don’t want to save within an ISA, or if you’ve saved £20,000 into your ISA this tax year (April 6th to April 5th the following year).
With a standard account, you won’t get any extra benefits (such as tax-free saving), but you don’t have to worry about paying tax until you sell your investments, and typically only if you’ve made more than £3,000 in profit (you might pay up to 20% tax).
Note: the government could change these tax rules in the future, and your overall tax treatment will depend on your individual circumstances.