[Orgmode] How can I search keywords in my org project?

[Water Lin]

I have used Org Mode to write a lot of stuff about my daily work, also
keep a lot of notes for my knowledge.

I build an org project as a wiki site for them. There are a lot of org
files.

So, here somes the problem. When I try to find something by keywords or
something else, what can I do? Is there any embeded search engine for
this work?

Or Can I use other way in Emacs itself?

Thanks

Water Lin

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