Xah Lee has a useful tutorial page on grep and grep-like searches from Emacs. The page is an old one but is worth bookmarking if, like me, you keep a list of valuable Emacs reference material. For some reason, I have difficulty remembering the material covered in the tutorial so it's really useful to me to have a quick link to it.
Lee covers how to use
lgrep from Emacs. That's pretty straight-forward, of course, but he also shows how to get the resulting file listed in a
dired buffer and how to search every marked file in
dired for a regular expression and then step through the results.
It's a short tutorial and worth taking a look at if you're not already familiar with using grep and grep-like searches from Emacs. You may also want to bookmark it so you have it handy for a quick review.