To begin your research, identify the major keywords that will help you find relevant information. Then, think of alternative search terms or synonyms e.g. pain relief may be referred to anaesthesia and labour may also be referred to as childbirth or labor. If you cannot think of any other terms, read a few articles on Summon, or read items on your reading list. You can also use a thesaurus to help you identify other search terms.
Be creative and think around your topic.
Use the Boolean operators AND and OR to modify your search. Make sure you put these terms in capital letters so that the software recognises them as Boolean operators - most search engines are programmed to ignore common words like these (and also things like the, of, in, etc.) so if they're not in capitals, they won't be used in the search.
AND narrows down the results by making sure the terms connected with it are guaranteed to be in the results e.g.:
infection AND prevention AND cannula
Using OR broadens the search out, by looking for terms that mean the same or similar things. Don't forget to use brackets to join any terms with OR e.g.:
(apnoea OR apnea) AND sleep
Putting an asterisk at the end of a word will search for various different endings e.g. anaesthe* will simultaneously search for anaesthetic and anaesthesia. However, do be aware that other words you don't want may be included, so be careful where you put the asterisk!
You can also use speech marks to search for phrases e.g. "respiratory tract infection" will find these words in this exact order and spelling, rather than finding the words individually (so you won't get information on infections in general).
If you need help using CINAHL, they have a lot of tutorials here. Also see below for the library helpsheet.
This Youtube video is great as a refresher on Boolean searching techniques.