I like Miro - I think there are lots of other options but in terms of getting started quickly and easily, it's hard to beat.

It's designed as an online whiteboard for collaboration - that you can share with others by sending them a link, (great for online teaching actually) but it's great just as a thinking tool to sort out your own ideas and then organise them visually.

I often screenshot what I've built and use that image in documents etc.

You can create a certain number of whiteboards free, but then need a subscription if you want more. They have a free educational license if you email them and ask - with proof of your educational-user status.

Canva and Figma are alternatives but Miro seems more intuitive to me.

Find it and have a play :-)

Matthew Lievesley Thank you for sharing. Will definitely visit all your suggestions.