Where are some instructions?

Simple: if your picture shows a shoe, enter shoe as the keyword and not car. Keywords should describe your object accurately. The suggested keywords are a good start, but you should clean them up. There is no gain, when your lake is in Sweden to accept Spain, just because the AI does not know much about geography.

Keywords are part of YOUR marketing strategy, you need to research and evolve your own approach. It's no good having rules or instructions, because if everyone does the same there is no differentiation. 

If you want to see what keywords work, which ones are ambigous, which ones have many hits, which ones have few, you can research this. A few thousand searches of Stock will not be time wasted.

Page 16 of the Adobe Stock Contributor Guide has some instructions on keywords. 

https://helpx.adobe.com/content/dam/help/en/stock/contributor/Adobe_Stock_Contributor_Guide.pdf

Mat Hayward, Adobe Stock Evangelist (an employee of Adobe) has also provided useful info on Titles and Keywords:

https://www.youtube.com/watch?v=DNYe84Wh_jg

Mat also provides webinars on many Adobe Stock topics which are very useful to beginners. You can find more info in the Discord community: https://discord.com/channels/692119372793118831/694260774532546700

Keywords are common sense search terms so people can find your image. 

If you care to post an image here, we will try to provide some suggestions.