There’s plenty of templates out there so think through why you’re doing it, what you want to use it for and who the audience would be. A lot of people spend too much time on a detailed plan when at their stage a regularly refined simple plan could be more effective. Make sure you create something that is useful to you, rather than just filling out someone else’s!
To help get started, one good site to start with a simple business plan on a page is the Business Model Canvas from Strategyser. There’s also lots of good resources to learn how to use it properly and next steps afterwards.
For Cashflow forecasts, a lot of the banks have templates to use. Business.govt.nz also has some others templates/resources (along with a Business Plan).