I have a list of strings like this:

["ra", "dec", "ra-error", "dec-error", "glat", "glon", "flux", "l", "b"]

I need to find all the strings in this list that contain "ra" or "dec" or "lat"

I checked many other threads as well as the regex manual. It turned out to be too confusing for me. Pleas help. :(

You don't need regex for this at all. A list comprehension with any will suffice

>>> subs = ['ra', 'dec', 'lat']
>>> strings = ["ra", "dec", "ra-error", "dec-error", "glat", "glon", "flux", "l", "b"]
>>> [s for s in strings if any(i in s for i in subs)]
['ra', 'dec', 'ra-error', 'dec-error', 'glat']