Understand the Difference Between a Stocks and Shares ISA and a Cash ISA

Cash ISA or Stocks and Shares ISA is one of the most common financial decisions in the UK and one that a lot of people make without properly understanding the difference. This explains both, when each makes sense for different timelines and goals, the risk trade-off in language that does not require a finance background, and the one mistake people make when picking between them.

I am confused about whether to use a Stocks and Shares ISA or a Cash ISA. Explain the actual difference, when each makes sense for different goals and timelines, the risk trade-off in plain terms, what the lifetime allowance situation is, and whether it makes sense to have both. Assume I know nothing about investing. I want to understand this well enough to make a decision, not to become an expert. Include the one mistake people make when choosing between them.