I would like to know one expression that means the same as "Going to the root of the problem..." Could, you please, let me know the expression and the meaning of it? Thank you in advance.
cut to the chase
"to talk about or deal with the important parts of a subject and not waste time with things that are not important" (source)
The grammatical context will dictate the kind of expression to use. There are dozens available but the one that occurs to me is "Getting down to the nitty-gritty", which I suppose means pushing aside vagueness, irrelevancy, distraction and other smokescreens and exposing the grit i.e. the hard, abrasive kernel of the matter. This is, however, not easy to use and requires a certain informality of context. Otherwise adverbs like "Basically", "Fundamentally", "In essence" at the beginning of an appropriate sentence could do the job.
One common idiomatic expression is...
...which is of uncertain origin, though there are several more or less fanciful theories. In my experience the primary sense is of addressing fundamental principles in a discussion, but it can also be used to mean getting serious or dealing with fine points of detail (in a barter/negotiation context).
Don't beat around the bush
See definition here
This is suitable in an informal context. To answer more thoroughly we would need more information