Introduced in Excel 2016, you can click into the “Tell me what you want to do” field as shown in the picture, or press Alt+Q from your worksheet, to enter a topic for information. This is a fairly intuitive new tool, while saving the interim step of hitting the F1 key for help about a topic.
For example, I typed “array formulas” into that field and the following information was provided.
What are its limitations? I found it does not help in all cases. Sometimes it does not return any cogent result.
I could not comment on what a sometimes cogent result is or isn’t, but as far as limitations go, that’s a question for Microsoft which can usually be found by doing a search, or contacting them directly, especially because it depends on what limitations you have in mind, such as search items, or character counts, or case sensitivity, or fuzzy matches, or whatever your concern is.