Select the fewest words possible to type into the search box -- just the ones most important to your topic.
Type AND between each new word or idea. For example: ukulele AND hawaii AND culture
ukulele AND hawaii AND community
skateboarding AND creativity
elvish AND language
elvish AND language AND internet
welsh AND language AND culture
The library catalog looks for the words you enter in just a few places (title, author, sometimes table of contents), so in most cases just typing in your general topic will work best (e.g., skateboarding, ballet)
Some of your topics might be too specific or new for using the library catalog to find books. In those cases, search for more general topics. For example, r/wallstreetbets is too recent/specific, but a search on stock market, hedge funds, or Reddit could provide context or other background information.
Limit your results to ebooks. After you do a search, look on the left for filters - use Availability > Full Text Online