I have read this sentence recently: "Formal exams are used to assess students at the end of each semester in many countries."
What i can't understand is : "are used to assess" does it indicate what it used to be used for in the past? or he is talking in general (present) that it is used for assessing?. I am grammatically confused.
There are (at least) three different senses of "used to".
In the first, simplest sense, "used" is simply the past tense of "use", but it may refer to an ongoing kind of use. This is the sense that is meant in your question. "Formal exams are used to assess students" is an example of "passive voice", which is often a way of talking about actions without mentioning who performs them. It means the same as "We use formal exams to assess students". This form is recognizable because of the passive construction and is not specific to "used to". You can find more examples on the Wikipedia page for passive voice.
The second sense refers to something that was true in the past but now isn't, e.g. "When I lived near the beach, I used to swim every morning" or "newspapers used to be more objective". This sense is more closely related to the word "usually".
The third sense refers to familiarity or peace with an ongoing occurrence, e.g. "At first I hated waking up at 6am every morning, but I'm used to it now." This sense is also related to the word "usually" and is recognizable because the argument is a verbal noun, "I am used to running long distances" or "I am used to singing in front of an audience".
More information here: https://dictionary.cambridge.org/grammar/british-grammar/past/used-to
The phrase "used to" sometimes takes on a life of its own, describing an activity that went on or a state that existed in the past and now has stopped. E.g., "My family used to vacation in Florida" means that in the past my family regularly went to Florida on vacation, and we no longer do. "She used to be my girl" means that at one time she was my girl (and that relationship had been going on for a time) and that now she no longer is. "I used to get the mumps" makes no sense because you only get the mumps once. "I used to have the mumps" makes little sense because you don't have the mumps for very long.
When used in this way, the combination is usually pronounced more like "use to" with a soft s. A possible substitute might be "formerly", though that doesn't necessarily imply an ongoing activity the way "used to" does. It is a somewhat informal phrase, but you have to change the sentence all around to make it sound more formal.
In the sentence you read, however, the phrase is used in the literal way. It might be rewritten "The way formal exams are used is to assess...", and in this case the phrase is pronounced "used to" with a hard s (like a z) and an audible d.
