Well, I will speak about school in the Basque Country. I guess it's the same in the rest of Spain, but I'm not sure and I warn you just in case.
1. We start school at the age of 3 more or less. It's 3 years of what we call "preescolar". At the age of 6, we start the primary school. Now it's called "Educación Primaria", but before it was EGB (Educación General Básica). There are six years: "primero de primaria", "segundo de primaria", "tercero de primaria", "cuarto de primaria", "quinto de primaria" and "sexto de primaria".
After that, pupils go to high school, in Spanish it's "el instituto". Kids are 11 or 12 years old. They must study there for 4 years and its called "ESO" (Educación Segundaria Obligatoria). Everyone in Spain must have the graduate (el graduado de ESO). If pupils aren't good enough or the don't like the high school, they have the chance to go to a CIP (Centro de Iniciativas Profesionales). There, they can get the graduate, but they have different subjects, more practical and they start learning a job.
After the ESO, people can start working or continue to study. If they continue, they have two opcions: they can continue in the high school and study "bachiller". Here they choose a branch of studies (sciences, letters or arts). It's 2 years. Then, if they want to go to university, they must do some exams called "Selectividad". The levels who get the highest qualifications choose first which degree they want to study.
If they don't want to study bachiller, they can do what we call "Grado Medio" in a centre of FP (Formación Profesional, something like profesional training). I'm not sure about that, I think it's 2 years or so, and then they can start working or continue studying, doing a "Grado Superior".
2. The English course hasn't got a very high level. We don't learn litterature. Sometimes, teachers ask us to read books, but they are very simple, usually adaptations made for students. Until last year, we studied grammar about all, and we trained ourselves on reading and writing, but we did very little of speaking. I don't know if that's changed this year.
3. / 4. In the "ESO", History and Geography are the same subject named Ciencias Sociales (Social Sciences). In first "bachiller", they are only compulsory for the ones who study Humanities. In second "bachiller", at least until last year, History was compulsory for everyone and we studied the 19th and the 20th centuries. In the "ESO", we study everything since the Prehistory. About, the Ancient World, Middle Age and so on, we study it in general, but then we pay more attention to the situation in Spain and in Basque Country. In 4th ESO, I remember studying the French Revolution and the nationalism in Germany and Italy. That is, we study about all Spanish and Basque History, but also some important event of other countries.
5. At school you can learn Spanish and Basque and have a bilingual education or learn only Spanish, but it's less common. About foreign language, most people study English. I started in 3th EGB, and it was compulsory. At high school, you must continue with English, but you can choose another language, usually French and sometimes (more rarely) German. At my high school, you could even give up studying English and take French as first foreign language but very few people do that.
I hope I make myself clear, I don't know because I wrote it quickly and maybe I didn't explain it well. If you have questions, just ask.