If you are working on a major project or long paper, you'll likely be conducting a multi-stage search for literature on your topic. You'll want to test the same search strings within different search engines and databases, and modify those strings after reviewing your results to see if any new papers appear. This can get unwieldy.
This is where a search log can come in handy. Keeping a log will help you to avoid unnecessary repetition of strings and save you valuable time. It will also provide you with a record of your searches in case you need to replicate them at a later date. This search log can be as simple as an Excel spreadsheet.
Helpful things to document include:
Take a look at this video from Southern Cross University Library on documenting and saving your search strategy for an example of a search log table.