Before you begin a database search, make sure you have a clearly defined PICO question.
Example: For adults with adhesive capsulitis, are electrotherapy modalities associated with improved function?
For additional guidance on formulating a research question, I recommend this article:
Aslam, S., & Emmanuel, P. (2010). Formulating a researchable question: A critical step for facilitating good clinical research. Indian journal of sexually transmitted diseases and AIDS, 31(1), 47–50. https://doi.org/10.4103/0253-7184.69003
Once you have your research question, it is helpful to break down your question into separate concepts. This will allow you to identify keywords for each element of your PICO question.
Concept 1 (population): adults
Concept 2 (additional population keywords): adhesive capsulities
Concept 3 (Intervention): electrotherapy modalities
Concept 4: (Outcome): improved function
Note: in order to make your search as comprehensive as possible, you may want to consider leaving out keywords that describe your outcome.