In North America, "High school" is the school that most students attend when they are aged 14-18 (grades 9-12). Typically, this results in a "high school diploma". This schooling is also called "Secondary school".
Note that this varies depending on the jurisdiction. For example, in Quebec, "Secondary" school is from grades 6-11.
From what Wikipedia tells me about the Tunisian educational system, the baccalauréat is a high-school diploma.
A Bachelor's degree is earned after secondary school (post-secondary) and is also known as an undergraduate degree. It is earned in universities or colleges (but again, the specific terminology depends on the jurisdiction: in Ontario, a college does not grant degrees).
You need to familiarize yourself with the educational system of the specific place whose system you wish to compare to. They are all different.