It depends on the journal...it will be mentioned for each journal if the published articles you want to read are open access or for free... and if you are an author it is also mentioned if you have to pay for publication or no...
A problem arises when it is not clear if a scientific journal is free or not after a closer look at its site. Unfortunately, I have seen such cases, although not so common. A letter or an email to the relevant journal may be the solution to this unpleasant situation, as pointed out by @Sajda Taha Mahmood. If they do not respond, try to search for another journal.
Can find this information at the journal's website under publication procedures OR under the section 'Instructions for Authors'. Sometimes it has a separate section all together. If it's unclear, contact the editor via mail.
Of course, you must ask the editor a question by email. If the answer is not followed within 3-5 days, then I do not cooperate with such journals and advise no one to cooperate with such journals.
You wrote, among others, in your second response that ''when we choose journals from the top ranked publishing group, we know that these journal are free for any submission or publication charges or fees...''.
As you may see below, ''free'' is not the universal rule for the cases you mentioned. Just an example of a Q1 journal (https://www.scimagojr.com/journalsearch.php?q=4700152228&tip=sid); I quote from its site: Molecular Systems Biology levies an Article Processing Charge (APC) of 3,300 EUROS (4,200 USD/GBP 2,750) plus tax, where applicable, for each Research Article, Method or Report accepted for publication... (http://msb.embopress.org/about).
''Dear Aristidis Matsoukis , why you ingore the rest of my response
"..... and if there is some payment which should be made by the author ( usually corresponding author) it will be mentionned in the authors guidelines of the journals ...."
And here I still talking about the top ranked journals (those ranked by Scimagi, SJR, SSCI. Clarivate...)''
Dear Ali Ahmadi,
Of course you are entitled to your opinion. I had decided not to proceed further after your second response. But after your response above, you let me no other choice. I want to believe that you understood that there is a contradiction in your second response between ''when we choose journals from the top ranked publishing group, we know that these journal are free for any submission or publication charges or fees'' and ''and if there is some payment which should be made by the author ( usually corresponding author) it will be mentionned in the authors guidelines of the journals, for this reason we need to publish with reputable journal.'' Both parts of this contradiction cannot be valid. This contradiction is my answer to your question ''why you ingore the rest of my response''. Certainly your last response put things in the right place and I believe that this is good for all of us. I think that everything is clear now.
Publishing houses should be very clear regarding the possible publication fees or other expenses for the publication of an accepted manuscript. In addition, the number of free journals is steadily reduced as time passes.