I'll introduce my favorite subject. I'll introduce my favorite subject.

I'll introduce my favorite subject. I'll introduce my favorite subject.

I'll introducem going to talk about my favourite subjetct at school. I'm going to talk about my favourite subject at school.

More natural English like this.

It wasused to be math when I doidn't learn graphs. It used to be math when I didn't learn graphs.

(1) "Was" is okay, but I think "used to be" is better. (2) It should be "didn't" and not "don't", since you're talking about a time in the past (when you learned graphs). I think that's what you meant at least. (3) It should be "graphs" and not "graph", since you're referring to graphs in general, rather than a specific one (presumably).

It was math when, although I don't learnike learning to graph. It was math, although I don't like learning to graph.

I hope I understood what you're saying here.

It was math when I don't learn graphs, though not if we were learning Geometry. It was maths, though not if we were learning Geometry.

Most of the English speaking world say "maths" though Americans say "math"! I assume you mean Geometry by "graph".

But my main favorite subject is mainly social sutudies. But my favorite subject is mainly social studies.

"Main favourite subject" doesn't sound very natural in my opinion.

But my main favorite subject is social sutudies because I like geography very much. But my main favorite subject is social sutudies because I like geography very much.

If feels more natural to combine this sentence with the next one, since the two ideas are directly related.

But my mainMy new favourite subject is sSocial suStudies. My new favourite subject is Social Studies.

Sentences don't start with 'but' in English and "main favourite" doesn't sound natural. Also is "studies" not "sutudies".

Because I like geography very much.

Bbecause I like geography very much. because I like geography very much.

If you mean you like SS because of the geography element the last 2 sentences would be combined into one. In English you never start a sentence with 'Because'.