Money you will need soon, such as within a year or two, is usually best kept somewhere stable and easy to access, because there may not be time to recover if markets fall just before you need it. Money you will not touch for many years can generally be exposed to more risk, because short-term ups and downs have time to even out and the long-term growth of assets such as shares has more chance to show through.
Matching your investments to your time horizon helps you avoid being forced to sell at a bad moment. An investor saving for a house purchase next year has very different needs from one saving for retirement several decades away, even if both are simply putting money aside. Being honest about when you will actually need the money is the starting point for a sensible plan.
This content is general information, not investment advice.