Depending on what they talk about? Do they have to have special permission or be apart of a leadership organization?
This really depends on your school. At mine, we get occasional emails about “President’s Office Hours” where anyone can show up, sign up, and get 5-10 minutes of one-on-one time to talk about anything. If you don’t have something like that, you can get in touch with the president’s administrative assistant to see if you can arrange something based on what you’d like to discuss.
I think only irregular students are allowed to meet with the Pres. 
My guess is if you proceed maturely, make an appointment, dress appropriately, have a smile, and are diplomatic, the President will be happy to speak with you.
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Is this something that should go up the “chain of command”? that is, if you are having a problem with a professor, have you talked to the Head of the Dept or the Dean of Students first?
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Does the President have open “office hours” where anyone can come?
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If not, make an appointment. But make sure they are the right person to address it. Maybe run your question/topic by a trusted adult at the college first.
At my college the president held gatherings based on major/department. I went to his house along with many other students and met him and his wife at a picnic. They lived in a huge university owned house in walking distance from the campus entrance. I also saw him at occasional campus events where he did go around and talk to students though mostly making small talk or about the current event.