To find terms that you want to search - you need to think broadly. You may want to do a quick search to find 2-3 papers on your topic then read these to see what terms they are using, acronyms (if applicable). You will to define your terms
See a couple examples below:
If you want to explore mental health in adolescence :
for mental health you would want to possibly search: anxiety, depression, bipolar, eating disorders, self harm, and suicide
for adolescence you would want to search: adolescence, adolescent, teen, teens, teenager, high school, young adult
Another example - you want to explore patients use of mobile apps:
for mobile apps you may want to search: mobile apps, mobile applications, Apple, Smartphone app, Cell phone app, Android, Facebook, X, TikTok, Instagram, etc.