There are four kinds of ISA: cash, stocks & shares, lifetime, and innovative finance. Over the course of the tax year, you can open one of each and split your allowance among them.
For example, you could invest £10,000 into your Saxo stocks and shares ISA, £5,000 into a cash ISA and £5,000 into an innovative finance ISA. Crucially, you cannot invest into two ISAs of the same category, such as two stocks and shares ISAs held with different providers.