Let's say you have a new business idea and you want to see if it is worth putting any more time into. You've told a few people about it and some say it's a good idea (maybe out of kindness) and some say it isn't. But none of that really means anything. So how can you start? Traditionally people suggest writing a business plan. These are 20+ page essays full of untested assumptions that take 80 hours to write. I know 'cause I've written them before. As Steve Blank says "No business plan survives first contact with customers." He suggests the lean startup approach, going the the loop of build->measure->learn->build, etc. developed by Eric Ries.
This became connected with the lean business model canvas. Here are slides on how to fill it out: https://www.slideshare.net/de-pe/lean-canvas-process-and-examples
The lean canvas fits the build measure learn loop. You build a solution to the problem, then measure the solution using the key metrics, from which you learn a more nuanced view of the problem and cycle continues.
I put together a template with examples in google docs here.
I have also found the Sequoia pitch deck format to be a useful starting place to think about whether a business idea has legs. Entrepreneurs often think a pitch deck is for investors, but that's not quite true. A good pitch deck should be written not to appease the investors, but as a way for an entrepreneur to dig through the important issues of a business in a way that the investor can start to evaluate if it make sense for them. You can't hide the main issues with your business; even a mildly savvy investor will be able to figure that out. So a good pitch deck is not written for the investor. It is written for the entrepreneur for the investor, if that make sense.
Below is a template for the Sequoia pitch deck and I've made a template in Google Drive that you can edit here.