If you are creating your charity's website from scratch, plan file names and directory structures carefully. The name of a file and the directory gives search engines an indication of what the page is about.
Search engines assume that the index.htm page is more important than other pages, so if you have a lot of information on a particular topic it is worth creating a separate, well-named directory for this information. If you look at the website of big charities they will generally have a complex directory structure with many subdirectories.
Try to think of one or two of keywords (preferably your target ones) that summarise the topic of the page and make that the filename, with hyphens between keywords.