With the help of a search string you will get the most versatile search possibilities when you are looking for comprehensive information on a certain topic.
As an example, a search about the topic "environmental effects of plastic waste".
An example search string:
"plastic waste" OR "litter plastic"
AND
environment* OR pollut*
In the example picture information has been searched on the environmental effects of plastic waste in Scopus database.
Picture: Scopus <https://www.scopus.com/search> 13.6.2018
In some databases it is recommended to use a command search (e.g. IEEE Xplore and ACM Digital Library).
First form a search string by using parentheses when searching for information on the environmental effects of electronic waste:
("electrical waste" OR "electronic waste" OR E-waste) AND (pollut* OR environment*)
Once the search string has been formed it is relatively easily transferable into different databases. It only needs to be modified based on the database's instructions if necessary, since e.g. operators, expressing a phrase and different inflections of words usually depend on the database.
In the example picture information has been searched on the environmental effects of electronic waste using the command search in IEEE Xplore database. Image source: https://ieeexplore.ieee.org/search 25.6.2018